Recent file code.
Change buggy qDeleteAll usage.
Starting on ViewScene/Spire hook-up
Removed boost from the source directory.

It will be checked out automatically by the cmake build system. I've
also added a .gitignore to the src/Externals directory indicating that
the boost directory should be ignored.
Populate recent file action list.
Hook up recent file menu to actions. Closes #98.
Closes #90: ? button launches help page in browser.
Closes #69.
Store file history in QSettings object. Closes #99.
#107: Added What's This button, some What's This text
Merge branch 'FixUnitTests'