Refactor key list state handling
as requested in !124 (comment 878615)
- State is now stored in a state config instead of a normal config
- Columns are now stored under a UUID instead of their ke
- Order of views is stored in an extra key instead of implicitely by sorting by name
- Main key list and certificate selection dialog views are stored in the same file
- Added migration logic to adapt to the new format
Note: The migration only works for the config format of the last released kleopatra version. The format used in recent git builds will not be migrated correctly.