MDL-43312 TinyMCE: Version bump to 3.5.10. Remove all the hacks.

I retested the old bugs that required custom hacks to tinymce and could not reproduce them,
so I have not reimplemented the hacks.
MDL-45410 Merge English strings from the en_fix language pack
MDL-45282 core_user: fixed up some oddities in the bulk user messaging screen
MDL-43119 Add valid until dates for tokens created by login/token.php

3 months were decided

Conflicts:
	login/token.php
MDL-45126 do not allow guests see name and summary of hidden course
Merge branch 'MDL-45410-en_fix-25' of git://github.com/mudrd8mz/moodle into MOODLE_25_STABLE
MDL-44750 Assign: Do not reveal student identities to screen readers
Merge branch 'MDL-45282_message_25' of git://github.com/andyjdavis/moodle into MOODLE_25_STABLE

Conflicts:
	theme/bootstrapbase/style/moodle.css
MDL-43312 TinyMCE: Reapply the z-index hacks (25 only)
MDL-43312 TinyMCE: Add back the upgrade instructions for z-index on 2.5
Merge branch 'MDL-43312-25' of git://github.com/damyon/moodle into MOODLE_25_STABLE
MDL-45414 wiki: blank image for page index icons