CATROID-1462 Change variable by "" brick does not work

[Rawbat]

Loop bricks now actually change their control variable instead of continually
setting it with calculated values. This allows for other change variable operations
inside the loop to have an effect.
This however furthers the possibility to create infinite loops and the resulting
value of the control variable after the loop is not as easily predictable when using
another change value operation inside the loop.

https://jira.catrob.at/browse/CATROID-1462

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[Hugoluk]

Changes look good. Added and adjusted test are also fine.
The test "ForVariableFromToActionTest" seems to through when running all unit tests, but fails when running alone. A ticket for this flaky test was created (CATROID-1559).

[JayTropper]

Everything fine for me!