feature(amd): added some utils to Elgg_Amd_Config class

Utils are unsetPath, unsetShim and removeDependency.
fix(amd): removed elgg_require_js for backwards compatibility

Use elgg_load_js instead. Use elgg_register_js to define sync or async
javascript instead.

`elgg_register_js` manages registrations and loadings of async js better
`elgg_unregister_js` also unregisters async js
`elgg_load_js` also loads async js
Removed `elgg_require_js` function and uses
New private function `_elgg_get_external_file_from_map`

Fixes #6496
chore(amd): added tests for AMD module registering and loading
chore(readme): Updated year and clarified MIT-X11 license

Fixes #5940
chore(amd): added docs for AMD modules
Merge pull request #6578 from sembrestels/readme-update-year-license

chore(readme): Updated year and clarified MIT-X11 license
Merge pull request #6497 from sembrestels/rm-elgg_require_js

Unify elgg_require_js and elgg_load_js
chore(html5shiv): Upgrade to html5shiv 3.7.0
chore(requirejs): Upgraded Require.js to 2.1.10
chore(markdown): upgraded php-markdown-extra to 1.2.8
chore(jquery): Upgraded jQuery to 1.11.0
chore(jqueryui): Upgraded jQueryUI to 1.10.4
chore(colorbox): Upgraded Colorbox to 1.4.36
chore(jquery-form): Upgraded jQuery Form plugin to 3.49.0