Altered:
- Refactored AMSortFilterWidget to be more self contained (now contains
its own widgets to control its hidden state, and present warnings to the
user to indicate its filtered state).
- Made the warning for how many scans the AMScanDataView was showing
more explicit, changed from "Data (Showing %1 scans)" to "Data (Filtered
to show %1 scans)"

Added:
- Class AMSortFilterBuilder ~ Represents the widgets that actually build
the filter. These are what are hidden when AMSortFilterWidget's Hide
button is clicked.