BookmarksFilteredByTagsSortProxyModel

Now it supports "not filtering".
Making it ready to be used as the default bookmark model.
Set filteredBookmarksModel as the permanent bookmarks model

Now BookmarksFilteredByTagsSortProxyModel filteredBookmarksModel; is a
MainWindow member. We ALWAYS use it instead of dbm.bms.model to
calculate model indexes.
Added invalidateFilter();  so the view updates itself

Call `invalidateFilter()` after changing the state. This causes the
`layoutChanged()` (on sorting) or `rowsInserted/Removed` (probably on
filtering) signals be emitted and be caught by the view using this
model, causing it to update itself. Without `layoutChanged()` the
Bookmarks view doesn't update itself.
Introduce MainWindow::RefreshStatusLabels

Also use `QString.chop(n)` instead of `QString =
QString.left(QString.length() - n)` :-)
Use RefreshUIDataDisplay to filter by tags

Instead of of RefreshTVBookmarksModelView in
MainWindow::lwTagsItemChanged; as it's more standard and also saves the
selection.
Introduced RA_NoRefreshView to improve performance

Used only when user checks/unchecks tags instead of the previous
RA_SaveCheckState mode.
Moved checked items restoring to their own function

Called MainWindow::RestoreCheckedTIDs
Added changelong and remaining TODOs