Added persistence of attributes for ScriptInstances in the editor, so that when an error occurs, the values are not reset to default.
- Added correct behaviour for undoing/redoing script attributes.
- Fixed drag slider undo/redo so that it creates a correct action representing old/new states.
Updated to cover these cases:
- Values are refreshed when scripts are changed.
- Loading/creating new scene clears the previously stored script attributes.
- Loading a scene will load the script attributes, so that if there was a script error after loading but before inspecting a ScriptInstance, the values are still known.
Merge remote-tracking branch 'remotes/hdunderscore/Editor_ScriptInstance_Persistance'
For Travis CI - switch CI build to use Raspberry-Pi build environment.