RE 7140_MantidEV_load_DetCal

Initial version.  Added controls for entering .DetCal
file names for two .DetCal files.  (The second file is
only needed for the second panel on SNAP.)
Added code to enable/disable the new controls properly.
Added code to save/restore the new controls' state properly.
Added code to record/save/restore names of most recently
used calibration files, so the file browsers for the
.DetCal files can start in that directory.
Factored out some common code for finding the directory
in which to start, based on a file name, placing it in
the method getFilePath().

refs #7140
RE 7140_MantidEV_load_DetCal

Place new controls for loading .DetCal file before the
controls for Max |Q| and selecting the Lorentz correction
so the order is consistent with the order in which the
algorithms are applied.
Also resetting the default state using the option on the
File menu will reset the .DetCal file names to blank.

refs #7140
Merge branch 'feature/7140_MantidEV_load_DetCal' into develop