fix(groups): forces content accessibility to members_only for invisible groups

When user selects "Group members only" for group visibility, javascript sets
the group content accessibility field to "Members only" and disables it.

For existing groups the above is done also on server side.

When editing an existing public group, a warning is added under the group
content accessibility input saying that changing the setting won't change
the access permission of existing group content.
fix(embed): file embedding wasn't working for textareas

Issue was introduced in 8b358c5 by removing the line that applies the text
change in textarea.

The way to extend javascript from the rich text editor was to extend a view
in js/embed/embed. It has been refactored to the 'embed', 'editor' js hook,
in order to make js/embed/embed convertible to js file. The view extension
has been deprecated.

Text areas and rich text editors manage the insertion diferently. In order
to insert the content in the correct place, we allow rich text editors to
return false inside the hook to stop the insert, and apply it just once.

Fixes #6160
chore(ui): Improved site secret UI for master after 1.8 merge.

Refs #6443
Merge pull request #6563 from brettp/site_secret_master

chore(ui): Improved site secret UI for master after 1.8 merge.
Merge pull request #6431 from juho-jaakkola/group_settings

fix(groups): forces content accessibility to members_only for invisible groups
Merge pull request #6547 from sembrestels/embed-textarea

fix(embed): file embedding wasn't working for textareas
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(cleanup): Changed aalborg manifest to use theme instead of template.
Merge pull request #6573 from brettp/theme_not_template

chore(cleanup): Changed aalborg manifest to use theme instead of template
chore(ui): added consistency to discussion edit reply view

Added label as in adding/editing comments
Added cancel button as in editing comments

Fixes #6421
Fixes #6302
Merge pull request #6575 from sembrestels/discussion-ui-edit-replies

chore(ui): added consistency to discussion edit reply view
chore(readme): Updated year and clarified MIT-X11 license

Fixes #5940
fix(lightbox): setting fancybox's z-index for colorbox
fix(embed): show error when when uploading too large file in embed form

Fixes #4591
Merge pull request #6579 from sembrestels/embed-uplaad-max-size

Embed upload max size
chore(embed): cleaned up a661c65c636272fd2a
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