Back Button Behavior in Object View #780

 When accessing a program either by using the "Continue" button on the Start Screen or through the Program List you are now
 always directed to the MyProjectsActivity when you use the Back button in the ProjectActivity.

 Changes:

 ProjectActivity.java: added intent for backwards navigation

 AndroidManifest.xml: added parentactivity to ProjectActivity for backwards navigation

 Fixed Testcases in following classes:
 FormulaEditorUserVariableFragmentTest
 LegoNXTTest
 MainMenuActivityTest
 MyProjectsActivityTest
 NewProjectDialogTest
Merge branch 'issue#780_backbutton_objectview' of github.com:Catrobat/Catroid into issue#780_backbutton_objectview