Add MathSlate TinyMCE plugin

Robert already submitted a patch for this under Bug 1464858, but since it's a separate plugin I'm spinning it off into a new bug.

Patch for master: https://reviews.mahara.org/#/c/4926/

Patch for "master" branch: https://reviews.mahara.org/4980

To test:

1) check that the $cfg->mathjaxconfig and $cfg->mathjaxpath variables are set in htdocs/lib/config-defaults.php

2) Go to admin -> configure site -> general settings and set Enable MathJax to 'on'

3) Create/Edit a page and add a 'text' block to the page

4) in the TinyMCE editor click the toggle icon (left of 'paragraph') to expand the options

5) Click the icon with hover state 'insert math' - it should open a popup titled 'Math Editor' that takes a few seconds to load

6) Click the third tab and click some upper and lower case greek letters - it should add your selection to the black background bit

7) Click insert line or insert display - the TinyMCE should be updated with some text, which may look a bit strange

8) Save the text block and the text displayed on the page should look like the greek letters you picked

Reviewed: https://reviews.mahara.org/4926
Committed: https://git.nzoss.org.nz/mahara/mahara/commit/325cdfac3dfba40efbbad8cd306dcfb385674709
Submitter: Jono Mingard (<email address hidden>)
Branch: master

commit 325cdfac3dfba40efbbad8cd306dcfb385674709
Author: Robert Lyon <email address hidden>
Date: Wed Jul 8 11:46:13 2015 +1200

Add tinymce4-mathslate plugin to tinymce in Mahara (bug #1472446)

behatnotneeded: 3rd party library

Change-Id: I16f196afb1a23d979db2811cf6fcf137cd8cae6f
Signed-off-by: Robert Lyon <email address hidden>

Patch for "15.10_STABLE" branch: https://reviews.mahara.org/5533

Reviewed: https://reviews.mahara.org/5533
Committed: https://git.nzoss.org.nz/mahara/mahara/commit/ae9a5fabed8d04d6aeff3225aa6c6cbc1a88f125
Submitter: Robert Lyon (<email address hidden>)
Branch: 15.10_STABLE

commit ae9a5fabed8d04d6aeff3225aa6c6cbc1a88f125
Author: Robert Lyon <email address hidden>
Date: Wed Jul 8 11:46:13 2015 +1200

Add tinymce4-mathslate plugin to tinymce in Mahara (bug #1472446)

behatnotneeded: 3rd party library

Change-Id: I16f196afb1a23d979db2811cf6fcf137cd8cae6f
Signed-off-by: Robert Lyon <email address hidden>
(cherry picked from commit 325cdfac3dfba40efbbad8cd306dcfb385674709)

Patch for "15.10_STABLE" branch: https://reviews.mahara.org/5534

Reviewed: https://reviews.mahara.org/5534
Committed: https://git.nzoss.org.nz/mahara/mahara/commit/e9e1d450180e1b7dac906f9a8ed7f53f1f4079d3
Submitter: Robert Lyon (<email address hidden>)
Branch: 15.10_STABLE

commit e9e1d450180e1b7dac906f9a8ed7f53f1f4079d3
Author: Robert Lyon <email address hidden>
Date: Fri Jul 17 18:14:50 2015 +1200

Making adjustments to the mathslate plugin for mahara (Bug #1472446)

1) Adding it to the tinymce if MathJax is enabled
2) Converting the uppercase Greek letters that have equivalents in standard alphabet
to those letters as MathJax doesn't adjust them

Change-Id: Ic7a524245f9602f0b2c78dc084a022a2fd3cb7c7
Signed-off-by: Robert Lyon <email address hidden>
(cherry picked from commit 99b8e799303308fa28e6ecfd50b04894b1af4ae5)