hack: dont commit

This is a hack, which makes it so that if nodrag is set on a block, we can't start a drag from the block (this essentially makes it immovable, unless an ancestor block is moved).

To use this hack
(1) pull down the branch
(2) from blockly do ./build_with_core
(3) open a level you're interested. find the blocks you want to mark as no drag, and do something like the following in the console (this works for frozen level 7 right now)
```
Blockly.mainBlockSpace.getAllBlocks()[2].nodrag = true;
Blockly.mainBlockSpace.getAllBlocks()[3].nodrag = true;