allow spaces in @ mentions

[KevinTriplett]

Pretty easy, but doesn't klose 1379 completely, so leaving that issue open...

It's still a little wonky, in that esc and multiple spaces doesn't entirely close it. And if left alone (ie no selection), then typing can cause it to pop back up <HI, I'M MISTER MEESEEKS! LOOK AT ME!!>

I think it's good enough for now, ya? I'll work on these two things next and separately, if they seem like the right things to do:

• limit to top ten (by id asc) w/scroll bar after 6 or so items
• scope by groups somehow (will need input on this one)

[tibetsprague]

hmm, actually this does not work well. you can never get out of autocompletion after typing a @! more work to do