added UMD capability to language file

First proposal as per #133 

I added an UMD header to the language file, so:

For commonJS on node it exports the language map:

````js
var tv4= require('tv4');
var lang = require('tv4/lang/de')
tv4.addLanguage('de', lang);
````

For AMD require the language map and add it:

````js
require(['path/to/tv4', 'path/to/tv4/lang/de'], function(tv4, lang){
    tv4.addLanguage('de', lang);
});
````

With globals it automagically adds itself to the global `tv4` (make sure to place after tv4.js):

````js
<script src="path/to/tv4.js">
<script src="path/to/tv4/lang/de.js">
````

As discussed we could opt to let the language file produce a decorated tv4 instance, but I think it is a bit messy (what if you'd use multiple languages or other extensions?). I think this solution is the cleanest with least magic (it would also fit well with how it works if users have their own language file somewhere).

As bonus I fixed #131 in the source, and changed the README badges to crispy SVG