Change `grunt avm1` and `grunt flash` to also build the relevant .abc files

... in parallel. If the `.as` files didn't change, then this doesn't take any time at all, and if they did, not building the `.abc` files is wrong.

Also removed the `playerglobal` and `avm1lib` aliases, as they're now subsumed in `flash` and `avm1`, respectively.
Merge pull request #1474 from tschneidereit/nat

Change `grunt avm1` and `grunt flash` to also build the relevant .abc files