log: deduplicate category names and improve logging.cpp

The code in `logging.cpp` needs to:
* Get the category name given the flag (e.g. `BCLog::PRUNE` -> `"prune"`)
* Get the flag given the category name (e.g. `"prune"` -> `BCLog::PRUNE`)
* Get the list of category names sorted in alphabetical order

Achieve this by using the proper std containers. The result is
* less code (this diff is +62 / -129)
* faster code (to linear search and no copy+sort)
* more maintainable code (the categories are no longer duplicated in
  `LogCategories[]` and `LogCategoryToStr()`)

This behavior is preserved:
`BCLog::NONE` -> `""` (lookup by `LogCategoryToStr()`)
`""` -> `BCLog::ALL` (lookup by `GetLogCategory("")`)

0 files changed, 0 insertions, 0 deletions