Show number of protocols whilst filtering

We also make tabs showing no protocols not visible. This also means that when searching, if you type an exact protocol name, you are moved onto that page.

Needs reworking, as when filtering is present but all protocols match the filter, the count isn't shown. This means Model will need to track the filter values itself (as they can't be retrieved from QSortFilterProxyModel) to know that filtering is being done to be used in the tab title.

Alternatively, we could show counts regardless of whether filtering, but this doesn't look right to me.