Refs #8284 Fix file extension filtering.
Refs #8284 Remove spacer from Fury interface.

This allows it to expand more naturally when resized.
Merge branch 'feature/8284_fury_convfit_data_selector' of github.com:mantidproject/mantid into feature/8284_fury_convfit_data_selector
Merge branch 'feature/8284_fury_convfit_data_selector' into develop