Revert "Add browserify ignore directive to package.json"

This reverts commit 482233a6392e4b204964dae050aa9d03283fbe41.
Preliminary commit for browserify compatibility

This is the first stage of my commits for issue #609 that will make the
npm module browserify friendly and browser friendly.

The grunt-browserify module has been introduced to replace
grunt-contrib-concat. Browserify automatically concatenates files and so
there is no need for a concat step.

The faye-websocket module was problematic so I moved the require out to
a separate module within the lib directory. The websocket module is a
folder containing a package.json, directing library consumers to the
entry point that is appropriate for their environment. Browserify picks
browser.js (which simply returns an object holding window.WebSocket)
while everyone else gets the faye-websocket module.

In addition, as browserify handles all the requires, there's no need to
detect the environment or include any pre-built modules. I've removed
the pre-built when and faye-websocket files in favour of letting
browserify use the modules within node_modules. This should make it
easier to maintain dependencies in future versions of this library.

One side effect of this browserify compatibility is that, in order to
allow the library to be globally available in the browser as `Mopidy`,
I've had to set Mopidy as the exported object instead of as a key of the
exported object. To elaborate further, the current API would be like the
following:

    var Mopidy = require('mopidy').Mopidy;

However, with this change, the API would be like this:

    var Mopidy = require('mopidy');

I'm not sure whether this would be an issue and so I think it's worth
discussing further. It's possible that node developers won't have a
problem but, if they did, a potential workaround within the mopidy.js
file would be:

   Mopidy.Mopidy = Mopidy;

This would allow developers to choose either of the following:

    var Mopidy = require('mopidy');
    var Mopidy = require('mopidy').Mopidy;

Could be a little odd to do this though