Adds some error checking to the GUI
Fixed interactive mode not working on Linux

gui/application.py:
  init: Fixed typo "elif", should be "if".
Removed faulty upgrades in examples/usersguide/mashups.vt

Ticket: 906
Merge branch 'v2.1'
Fixes typo in docs
Adds missing tag "contour 4" to mashups.vt
Usersguide: Use "contour 3" in mashups example
Merge branch 'v2.1'

Conflicts:
	doc/usersguide/mashups.rst