Upgrade 3rd party plugin CSSTidy for php 7.2

[Rebecca Blundell]

related to https://bugs.launchpad.net/mahara/+bug/1752743

CSSTidy is currently at version 1.5.5, 1.5.7 looks like it replaces functions deprecated in php 7.2, although I haven't comprehensively checked it and the github page is not specific, just says it has changes for php 7.0.

https://github.com/Cerdic/CSSTidy

[Mahara Bot (dev-mahara)]

Patch for "master" branch: https://reviews.mahara.org/8976

[Steven (stevens-q)]

Environment tested: Master
Browser tested: Chrome

-------------------------------------
Manual Test Script
-------------------------------------

Preconditions:

1. Institution member "InstAMember" exists
2. User created skin exists as follows:
----- a. Skin title = Some Skin name
----- b. Custom CSS = p {display:block;color:#639;font-size:11px}

Test Script: User creates portfolio page and uses "Some Skin name" skin to give page text a purple colour

1. User creates a portfolio page as follows:
----- a. Page title = Skins testing CSSTidy
----- b. Skins = Some Skin name
2. User adds a text block to the page
3. User click "Display page" button
4. Confirm that the text colour of the text block is indeed purple ✔

Catalyst QA Approved ✔

[Mahara Bot (dev-mahara)]

Reviewed: https://reviews.mahara.org/8976
Committed: https://git.mahara.org/mahara/mahara/commit/79bac249ca16cb650582a3a8c426bfaf6ce61fe9
Submitter: Robert Lyon (<email address hidden>)
Branch: master

commit 79bac249ca16cb650582a3a8c426bfaf6ce61fe9
Author: Rebecca Blundell <email address hidden>
Date: Tue Jun 26 16:23:30 2018 +1200

Bug 1773891: Update csstidy to 1.5.7

includes compatibility changes for PHP 7.2

behatnotneeded

Change-Id: Ifd0b988cd513bd327ea7cf08b434788916f150b9