Reference MGScopeBar class to prevent linker from stripping it

We instantiate the class in the xib file, so the linker does not know that we actually need it.

Currently the filter list framework use MGScopeBar, which is why this issue is not an actual problem (yet).
Implement intrinsicContentSize for OakKeyEquivalentView

This will allow it to be used with constraint based layouts.
Make OakChooser’s cancel: method public API