[FIX] Refactor and simplify import/export

[EmmaTellblom]

Redo the entire import/export handling.

Split Mensinator Import and Export to two different classes to simplify the processes. (Should we split the ExportImport dialog as well?)

SettingsScreen interacts with ImportExportDialog and also SettingsViewModel (for the settings directly in settingsscreen).
SettingsViewModel uses MensinatorExport and ClueImport (and if other imports have been added, them too)

Will add image of this later, this is just to remember.

[EmmaTellblom]

The viewmodel should not send Toast to UI (ExportImport). VM should only return indicators (either messages to be displayed to user, or true/false and let ExportImport handle Toast)

[EmmaTellblom]