For #25952 - Fixed PyQt compatibility issue
Some old versions of PyQt don't have the Q*Animation classes that were introduced in Qt 4.6
Closes #91
#25983 Added null-check in environment to better support empty engines.
This fixes an issue where it was previously not possible to install apps
into some empty engine config setups.
Merge branch 'master' of ssh://github.com/shotgunsoftware/tk-core
Merge branch 'master' into 25760_setup_project_wizard