Make it easier to do clean builds

[HamzaRino]

Currently in order to do clean build we need to set the BuildOption flag CleanBuildCache from the respective BuildCollection.
But we do not want to have to do this every time or have two build configs one clean and one normal.

I suggest we expose a "Clean Build" button for the Build Collection and a command parameter (-clean) when we execute UBS from Unity in match mode.