Revert "MDL-38387 cache: fixed inifinite initialisation loop with site id"

This reverts commit 17200a016dba8479476a3819b5646855014b8d75.
MDL-38467 import YUI 3.9.0
weekly release 2.5dev
MDL-38490 question preview, variant is attempt (not display) option
MDL-38397 question editing: only validate default mark if present.

Most qtypes have that field, but not all. multianswer is an example in core.
Also some contrib qtypes.
MDL-38355 qtype_multianswer: input boxes too big in Russian.

... and any other language where the characters take multiple
bytes in UTF-8.

This fix was worked out by Dušan Ristić. I am just committing it.
MDL-38388 qformat_blackboard_six: fix question image import

This works on the expectation that the returned array from readdata()
is opaque and will be fed directly into readquestions() since
filebase is different per file and needs to be set up appropriately
before each parse.
MDL-38497 Nodes can be put before a sibling in the admin tree

The patch introduces a new optional parameter of the add() method for
all classes implementing the parentable_part_of_admin_tree interface.
Currently we have only one class admin_category implementing this
interface. If some third party code implements this interface too, they
will get an error and will have to fix the add() method signature.
However, the chance that such third party code exists is considered
pretty low.
MDL-38497 Add unit tests for the admin tree behaviour
MDL-38497 Add the info about the method signature change into upgrade.txt
MDL-38497 Fix invalid $ADMIN->add() calls

As the admin_category::add() method now checks for the third parameter,
couple of typos were detected in the code. Additional parameters passed
to the add() method were probably a mistake, a relict or a typo.

Note that the typo in admin/tool/unsuproles/settings.php had actually
significant impact on the functionality as the array with required
capabilities was not actually passed to the admin_externalpage
constructor as intended.
Merge branch 'MDL-38474-master' of git://github.com/FMCorz/moodle
MDL-38005 form: Headers have a proper name
MDL-38474 repository: Cannot edit a repository instance
Merge branch 'MDL-38474-master' of git://github.com/FMCorz/moodle
MDL-38395 question categories: wrong URLs after editing.

The problem was that array1 + array2 takes the values from
array1 when a key appears in both places.

While working on this area, I updated it to use html_writer.
MDL-35875 - User - Modify the profile page to use semantic HTML rather than tables for layout
MDL-35875 themes: Safe multiline topics on profile
MDL-38363 qtype_calculated. Fix warnings.
MDL-38412 fix quiz reports group mode weirdness.

Moodle currently selected group uses the session. This can cause weird
effects when you have two tabs open. This is particularly weird in the
quiz reports, where some actions like delete attempt are checked against
the currently selected group.

The solution is to put the currently selected group into the URL for all
actions like delete/regrade attempt, regrade all attempts, download and
sort table.