Adds warnings for uncallable handlers in hooks/events.
Adds units for the warnings.
Injects logger into events/hooks services.
Ensures logger, events, and hooks are setup in right order in service provider.
Fixes small bug in DI container.
feature(views) Eases extending the input/view view

In order to extend forms *outside* the form element, devs must extend the 
input/form view, however it's a bit cumbersome to determine the current
action because you have to extract it from the "action", which is a URL. This
gives the extending view the raw action name.

Fixes #6129
security(http): Adds anti-clickjacking header when serving pages

Adds a header that prevents framing pages from different domains in
modern browsers. A plugin hook allows disabling/altering the headers
sent.

Fixes #6098
fix(embed): make pagination in embed colorbox usable

View mod/embed/views/default/embed/list.php is missing a base_url for navigation.

Adding 'base_url' => elgg_get_site_url() . "embed/" to the options for pagination fixes this

Refs: Issue #6357
Merge pull request #6265 from mrclay/uncallable_handlers

Adds warnings for uncallable handlers in hooks/events.
Merge pull request #6348 from mrclay/6129

Eases extending the input/view view
docs(hooks): Corrects docs syntax error
Merge pull request #6380 from Srokap/pr/6331
fix(lightbox): lightbox wasn't shown when generated from ajax view.

It also fixes page owner in core/edit_comment ajax view, needed for a consistent
experience with embed plugin.

Fixes #6304
feature(output): Added second parameter to elgg_strip_tags.
Merge pull request #6324
fix(embed): Allows embedding files from the containing group

If the user is a member of the group containing the host entity, this allows
the user to embed files from that group via the lightbox.
fix(views): Correct default title for confirmlink

Wrong key was used from $vars when 'title' was not passed.
It now correctly defaults to 'confirm'.

Closes #6375
Merge pull request #6376 from hellekin/fix-6375

Fix wrong key from $vars (closes #6375)
fix(lightbox): Correctly applies color box options on each element

Whatever colorbox options were on the data- attribute of the first element
get copied to all the other elements. This fixes that.

Fixes #6107
Merge pull request #3 from mrclay/sembrestels-embed-editing-comment

fix(lightbox): Correctly applies color box options on each element
feature(graphics): make logos transparent

Adds transparency to branding

#6398
Merge pull request #6399 from hypeJunction/logos

Fixes #6398: make logos transparent
Merge pull request #6384 from mrclay/slyhne-patch-7

Fixes pagination and group file finding in embed
Merge pull request #6378 from sembrestels/embed-editing-comment

fix(lightbox): lightbox wasn't shown when generated from ajax view.