Split out the actual filtering from the MultiFilterSortModel.
Create a DiveFilter class that does the actual filtering.
Currently, mobile and desktop have their own version of this
class, though ultimately we may want to merge them.
The idea here is that the trip-model and undo-commands have
direct access to the filter-function and thus can take care
of keeping track of the number of shown dives, etc.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>
The filter-model was catching dives-added / dives-deleted signals
from the models to keep track of the number of shown dives.
To simplify the data flow, do this directly in the undo-command.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>
In the future we might want to use undo-commands for mobile as
well (even if not implementing undo).
Therefore, move the undo-command source from desktop-widgets
to their own commands top-level folder.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>