Refactor load current project

Concerning #452 

This branch introduces a new LoadProjectTask, which loads a project and shows an ProgressDialog to give the user a visual feedback that Pocket Code is doing something.

Further the current project is NOT loaded on app start anymore, it will be loaded when the user clicks on the "Continue" button (with visual feedback).

Jenkins Testrun: (Webtests are failing randomly)
http://jenkins.catrob.at/job/Catroid-custom-branch-no-emma-test/200/console
Ui Package web tests:
http://jenkins.catrob.at/job/Catroid-single-UI-package-test/179/console
UploadDialogTest:
http://jenkins.catrob.at/job/Catroid-single-UI-test/991/console