Filter presets are now displayed as buttons under the main menu. Left click activates the preset filter, right click removes the preset.
Saved dates changed into yyyy-mm-dd format, time is discarded. Filtering books by dates now works correctly.
Optimized UsbSync and added progress bar for synchronization
Added empty language option for language comboboxes
Removed unused imports
Fixed infos displaying in default system language, when triggered from separate thread
Merged SQL code for database structure creation into one query