Starting post requests
Option to post now working and showing result in a modal

- Included information about cross-domain requests in the README
- Organized the js a bit better, with a class
- Added a content-type to the html, removed js warning

refs #540
Update bootstrap to version 3.0.3

Version downloaded directly from http://getbootstrap.com
Includes several adjustments in the interface to make it look nicer with
this new bootstrap.
Prettier modal with useful information for POST success/error

Show some actually useful information if a POST request fails. Highlights the
most common problem: user does not allow cross-domain requests.

refs #540
Group configurations in retractable panels

Reduces a bit the number of components in the screen and will open space for
new items to be included for posting data.
Expand links using css only

Removing styling from the js and improved the appearance of expanded links
a bit.
Finish basic preupload of slides using a url

Accepts a single url with content to preupload.

refs #539
Pre-upload of slides only using URLs, allow multiple values

Accept multiple URLs and uses them all when send 'create' requests via POST.
Removed the components to upload slides via content set in an input. Doesn't
make much sense to set the entire content of an image or pdf in an input.

refs #539
Update bigbluebutton-api-js to mconf/bigbluebutton-api-js@64c522f10348e
Add new parameters supported by BigBlueButton 0.81
Update the link to Mconf-Live's API docs
Slightly change in the thanks message in the header
Improve the padding method to make it more generic and consistent
Remove compiled files from master, keep them only on gh-pages

gh-pages will store the compiled files for the latest version.
Allow setting the text of a config.xml for setConfigXML

Updated bigbluebutton-api-js to 9bb6b9fdd2fb.
Had to adapt the calls to bigbluebutton-api-js that have changed.

Note: For now the config.xml content is passed in the URL when setConfigXML
is called and not in the body of the POST call. This has to be double checked.

refs #1110
Ignore .nvmrc
Signal setting data for config.xml as experimental

Not thoroughly tested yet, might still have some issues.

refs #1110