Remove executable path setting for programs.

This should just be specified in the executable field.

Change-Id: Ic927143bac83c5b0d5fa4fe57220786dd2516f70
Use the FileBrowserWidget in the program config GUI.

If configuring a program for a local queue, use the
FileBrowserWidget (ported from Avogadro) to prompt and
validate the executable name. A QLineEdit is used for remote
queues.

Change-Id: I087da11ee1d2bfd0de8aaae710f1c733ef973757
Check path for executable files.

Change-Id: I6365f261765a00047f2b3c9358573b2354ebbbbd
Merge topic 'remove-program-path' into master

f4edacd2 Check path for executable files.
e5989799 Use the FileBrowserWidget in the program config GUI.
0b1972e5 Remove executable path setting for programs.