tag system for payments

Created by: deadlocker8

• additional table "tag", additional table "tag_match" (columns: payment_ID, tag_ID
• add server endpoints
• add database queries
• add unit tests for database queries
• add to new/edit payment UI
  • add existing tag
  • allow creation of new tag on the fly #177 (closed)
• add to report
• adjust filter settings
• add to search
• handle import/export --> handle older versions?
• flowpane doesn't resize
• save new tags overwrite old ones
• filter active icon not showing if filtered by tags
• delete tags that are not referenced