Re 6687 MantidEV menubar

Implemented Save and Load for Isaw Peaks and UB matrix
on menu bar.  Also added option to just index using
the current UB matrix (if any).
Refs #6687
Re 6687 MantidEV menubar, save/load settings.

The settings of all GUI controls are now automatically saved
in a default location, and can be optionally saved and
loaded from a user specified file.  This is implemented
using Qt's QSettings object.

Refs #6687
Re 6687 MantidEV menubar, show UB

Implemented the menubar item View->ShowUB.
The UB matrix is displayed using g_log.notice(),
both in the internal "Mantid" format and in the
external "ISAW" format, along with the lattice
parameters.

Refs #6687
Re 6687 MantidEV menubar, clean up code

Removed print statements left over from when the methods
were just "stubs".  Fix variable scope style flagged by
CPP check.

Refs #6687
RE 6687 MantidEV menubar, clean up code -- 2

Added Doxygen comments to all methods.
Delete local thread pool in the destructor.

Refs #6687
Merge remote-tracking branch 'origin/feature/6687_MantidEV_menubar'