Unit test testdata assets should be able to be changed and regenerated

Currently the unit test testdata assets are binary only, so modifying them is really hard. Also, having the "raw" test data available can make it easier to understand what each specific test is doing.

There's two alternatives how this could be achieved:
1) Have all the assets in non-compressed format next to the testdata, such as testdata_raw. Then some QSR tool could convert all that raw data to compressed data with simple instructions for user.

2) Generate all test data with code at the start of the unit testing such. EventHandler does this right now by creating a qml layout using test helper functions.