add testem commands for watch

[gnarf]

Allows testem to just launch it's chrome and show tests in terminal.

[dgeb]

Hmmm ... seems to break Travis https://travis-ci.org/orbitjs/orbit.js/builds/55664790

[gnarf]

So I made some tweaks, and now I can't get it to run in "watch mode" myself...

Something about changing the cwd causes it to error out with:

015-03-25 08:56 node[34875] (FSEvents.framework) FSEventStreamStart: register_with_server: ERROR: f2d_register_rpc() => (null) (-21)                                  2
Error: watch EMFILE
    at exports._errnoException (util.js:746:11)
    at FSEvent.FSWatcher._handle.onchange (fs.js:1161:26)

[gnarf]

Okay you can testem -l chrome to test in a specific browser in watch mode.

[gnarf]

Pretty sure I got this stable for travis and for node_modules/.bin/testem -l chrome mode

[dgeb]

I like it - thanks @gnarf!