fix webtests

some webtests are unstable - they fail randomly, e.g.
http://catrobatgw.ist.tugraz.at:8080/job/Catroid-no-emma/59/

I did a testrun of ProjectUpAndDownloadTest with 10 iterations:
http://catrobatgw.ist.tugraz.at:8080/job/Catroid-single-UI-test/913/console
sometimes there are 4 and 2 errors

after adding FlakyTest with tolerance 4, the console output looks way better:
http://catrobatgw.ist.tugraz.at:8080/job/Catroid-single-UI-test/915/console

only one testcase is failing - but this test will be fixed separately.
I think it is worth a try to get closer to "green" builds on Jenkins :)