Do Not Save Translation for Filters in Settings Session

[ShaopengLin]

From #1175 comment

1. We should only need to store a list of strings, the filter keys, in the session. The problem comes with backward compatibility as the previous sessions are now invalid. Need to discuss how to best approach this issue.

2. KiwixChoiceBox needs to adapt to the new session management.

[kelson42]

@ShaopengLin If you don't migrate, the only problem is that people will loose once their categorisation filters, just after software upgrade, right? To me I don't really understand why we should not implement straight this in a PR. Seems trivial.

[ShaopengLin]

@kelson42 @veloman-yunkan if we are ok with that one time lost, then indeed we can make this change directly. This then should come with #1175, as it will not introduce a huge detour. If you all agree could you close this? I will make the modification back over at #1175.

[veloman-yunkan]

Fixed by #1175