Adding file type option to ConvFit tab.

Refs #4870
Fixed merge conflict with another branch I was working on.

Merge commit '184fc6adecdf01bad218c036783e035970f7c9fe' into feature/5590_IDA_support_workspace_refresh

Conflicts:
	Code/Mantid/MantidQt/CustomInterfaces/inc/MantidQtCustomInterfaces/IndirectDataAnalysis.ui

Refs #5590