Blocks menu

I've written a drop-down menu for inserting scratchblocks, based on suggestions from [Lightnin](http://scratch.mit.edu/users/Lightnin/#comments-316259) and feedback [from the forums](http://scratch.mit.edu/discuss/topic/14779/).

It allows the user to select blocks from a list similar to the Scratch 2.0 interface. After selecting a block, it places the cursor inside the first input slot, ready for the user to type into. It also includes a link to the wiki article on the syntax.

This should help make the scratchblocks feature more discoverable. It still has some minor glitches, but I think these can be fixed later.

I've also updated the scratchblocks2 plugin to the newest version.