Merge bitcoin-core/gui#4: UI external signer support (e.g. hardware wallet)

1c4b456e1a0ccf0397d652f8c18201c3224c5c21 gui: send using external signer (Sjors Provoost)
24815c6309431cb0797defaf7add1150bcf4b567 gui: wallet creation detects external signer (Sjors Provoost)
3f845ea2994f53e29abeb3fa158c35f1ee56e7e8 node: add externalSigners to interface (Sjors Provoost)
62ac119f919ae1160ed67af796f24b78025fa8e3 gui: display address on external signer (Sjors Provoost)
450cb40a344605dda3bcc39495c35869580b9fc2 wallet: add displayAddress to interface (Sjors Provoost)
eef8d6452962cd4a8956d9ad268164715365b9ab gui: create wallet with external signer (Sjors Provoost)
6cdbc83e9341d1552faee4ccd8c190babc63e8d1 gui: add external signer path to options dialog (Sjors Provoost)

Pull request description:

  Big picture overview in [this gist](https://gist.github.com/Sjors/29d06728c685e6182828c1ce9b74483d).

  This PR adds GUI support for external signers, based on the since merged bitcoin/bitcoin#16546 (RPC).

  The UX isn't amazing - especially the blocking calls - but it works.

  First we adds a GUI setting for the signer script (e.g. path to HWI):

  <img width="625" alt="Schermafbeelding 2019-08-05 om 19 32 59" src="https://user-images.githubusercontent.com/10217/62483415-e1ff1680-b7b7-11e9-97ca-8d2ce54ca1cb.png">

  Then we add an external signer checkbox to the wallet creation dialog:

  <img width="374" alt="Schermafbeelding 2019-11-07 om 19 17 23" src="https://user-images.githubusercontent.com/10217/68416387-b57ee000-0194-11ea-9730-127d60273008.png">

  It's checked by default if HWI detects a device. It also grabs the name. It then creates a fresh wallet and imports the keys.

  You can verify an address on the device (blocking...):
  <img width="673" alt="Schermafbeelding 2019-08-05 om 19 29 22" src="https://user-images.githubusercontent.com/10217/62483560-43bf8080-b7b8-11e9-9902-8a036116dc4b.png">

  Sending, including coin selection, Just Works(tm) as long the device is present.

  ~External signer support is enabled by default when the GUI is configured and Boost::Process is present.~

  External signer support remains disabled by default, see https://github.com/bitcoin/bitcoin/pull/21935.

ACKs for top commit:
  achow101:
    Code Review ACK 1c4b456e1a0ccf0397d652f8c18201c3224c5c21
  hebasto:
    ACK 1c4b456e1a0ccf0397d652f8c18201c3224c5c21, tested on Linux Mint 20.1 (Qt 5.12.8) with HWW `2.0.2-rc.1`.
  promag:
    Tested ACK 1c4b456e1a0ccf0397d652f8c18201c3224c5c21 but rebased with e033ca1379, with HWI 2.0.2, with Nano S and Nano X.
  meshcollider:
    re-code-review ACK 1c4b456e1a0ccf0397d652f8c18201c3224c5c21

Tree-SHA512: 3503113c5c69d40adb6ce364d8e7cae23ce82d032a00474ba9aeb6202eb70f496ef4a6bf2e623e5171e524ad31ade7941a4e0e89539c64518aaec74f4562d86b

1 files changed, 14 insertions, 0 deletions

diff --git a/src/qt/walletcontroller.cpp b/src/qt/walletcontroller.cpp
index aa26a01541..7e5790fd87 100644
--- a/src/qt/walletcontroller.cpp
+++ b/src/qt/walletcontroller.cpp
@@ -263,6 +263,9 @@ void CreateWalletActivity::createWallet()
     if (m_create_wallet_dialog->isDescriptorWalletChecked()) {
         flags |= WALLET_FLAG_DESCRIPTORS;
     }
+    if (m_create_wallet_dialog->isExternalSignerChecked()) {
+        flags |= WALLET_FLAG_EXTERNAL_SIGNER;
+    }
 
     QTimer::singleShot(500, worker(), [this, name, flags] {
         std::unique_ptr<interfaces::Wallet> wallet = node().walletClient().createWallet(name, m_passphrase, flags, m_error_message, m_warning_message);
@@ -291,6 +294,17 @@ void CreateWalletActivity::finish()
 void CreateWalletActivity::create()
 {
     m_create_wallet_dialog = new CreateWalletDialog(m_parent_widget);
+
+#ifdef ENABLE_EXTERNAL_SIGNER
+    std::vector<ExternalSigner> signers;
+    try {
+        signers = node().externalSigners();
+    } catch (const std::runtime_error& e) {
+        QMessageBox::critical(nullptr, tr("Can't list signers"), e.what());
+    }
+    m_create_wallet_dialog->setSigners(signers);
+#endif
+
     m_create_wallet_dialog->setWindowModality(Qt::ApplicationModal);
     m_create_wallet_dialog->show();