Deduplicate bitcoind and bitcoin-qt init code

Add common InitConfig function to deduplicate bitcoind and bitcoin-qt code
reading config files and creating the datadir.

There are a few minor changes in behavior:

- In bitcoin-qt, when there is a problem reading the configuration file, the
  GUI error text has changed from "Error: Cannot parse configuration file:" to
  "Error reading configuration file:" to be consistent with bitcoind.
- In bitcoind, when there is a problem reading the settings.json file, the
  error text has changed from "Failed loading settings file" to "Settings
  file could not be read" to be consistent with bitcoin-qt.
- In bitcoind, when there is a problem writing the settings.json file, the
  error text has changed from "Failed saving settings file" to "Settings file
  could not be written" to be consistent with bitcoin-qt.
- In bitcoin-qt, if there datadir is not accessible (e.g. no permission to read),
  there is an normal error dialog showing "Error: filesystem error: status:
  Permission denied [.../settings.json]", instead of an uncaught exception

1 files changed, 2 insertions, 0 deletions

diff --git a/src/Makefile.am b/src/Makefile.am
index 72e7db5334..7dc5594cf2 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -134,6 +134,7 @@ BITCOIN_CORE_H = \
   clientversion.h \
   coins.h \
   common/bloom.h \
+  common/init.h \
   common/run_command.h \
   common/url.h \
   compat/assumptions.h \
@@ -640,6 +641,7 @@ libbitcoin_common_a_SOURCES = \
   chainparams.cpp \
   coins.cpp \
   common/bloom.cpp \
+  common/init.cpp \
   common/interfaces.cpp \
   common/run_command.cpp \
   compressor.cpp \