Add additional filters. Cache filter index for reuse next time
dialog is shown.

Add member to create individual filters and member to concatenate
individual filter for dialogs filter.

Converted members to local functions since both members are used in only one
location. They can only be used within the containing member and simplifies
the member list on the type.

Caches filter index last chosen for next import. Filter index is saved
to config file to continue using last chosen index went starting a new
instance of RD.

When filter index matches cached/config index no save occurs.
When filter index differs from cached/config index save occurs.

Cancelling an import does not change filter index. Saving does not occur.

Restore inital null check and model mockProjectSettingsProvider after it.
Constructor inject dependencies.

…or_synchronizing_document_types