The Database, DatabaseWidget, and DatabaseTabWidget classes share many responsibilities in inconsistent ways resulting in impenetrable and unmaintainable code and a diverse set of bugs and architecture restrictions. This patch reworks the architecture, responsibilities of, and dependencies between these classes.
The core changes are:
* Move loading and saving logic from widgets into the Database class
* Get rid of the DatabaseManagerStruct and move all the information contained in it into the Database
* Let database objects keep track of modifications and dirty/clean state instead of handing this to external widgets
* Move GUI interactions for loading and saving from the DatabaseTabWidget into the DatabaseWidget (resolves#2494 as a side-effect)
* Heavily clean up DatabaseTabWidget and degrade it to a slightly glorified QTabWidget
* Use QSharedPointers for all Database objects
* Remove the modifiedImmediate signal and replace it with a markAsModified() method
* Implement proper tabName() method instead of reading back titles from GUI widgets (resolves#1389 and its duplicates #2146#855)
* Fix unwanted AES-KDF downgrade if database uses Argon2 and has CustomData
* Improve code
This patch is also the first major step towards solving issues #476 and #2322.
* Create history-based merging that keeps older data in history instead of discarding or deleting it
* Extract merge logic into the Merger class
* Allows special merge behavior
* Improve handling of deletion and changes on groups
* Enable basic change tracking while merging
* Prevent unintended timestamp changes while merging
* Handle differences in timestamp precision
* Introduce comparison operators to allow for more sophisticated comparisons (ignore special properties, ...)
* Introduce Clock class to handle datetime across the app
Merge Strategies:
* Default (use inherited/fallback method)
* Duplicate (duplicate conflicting nodes, apply all deletions)
* KeepLocal (use local values, but apply all deletions)
* KeepRemote (use remote values, but apply all deletions)
* KeepNewer (merge history only)
* Synchronize (merge history, newest value stays on top, apply all deletions)
