FIX Overriding of theme templates in project folder

Fixes issue of templates not being found when a Page's main/Layout templates are split between the project and theme folders. Adds more expansive testing for template loading.
FIX Escape the redirect URL before outputting

Signed-off-by: Stephen Shkardoon <stephen@silverstripe.com>
Issue 1603, rewrote first sentence - uses the php curl lib

Issue 1603, rewrote first sentence - uses the php curl library, enabling connections to remote web services
Merge pull request #2969 from mrsmuneton/3.1

Issue 1603, rewrote first sentence - uses the php curl lib
Fixing FormField not setting readonly attribute on setReadonly(true)
Merge pull request #2776 from ryanwachtl/fix-get-candidate-template

FIX Overriding of theme templates in project folder
NEW: Show loading indicator when attaching files to UploadField
Merge pull request #2914 from kinglozzer/uploadfield-attach-loader

NEW: Show loading indicator when attaching files to UploadField
BUG Fix issue with versioned dataobjects being cached between stages
Merge pull request #2983 from tractorcow/pulls/3.0-fix-versioned-partialcache

BUG Fix issue with versioned dataobjects being cached between stages
BUG Fix encoding of JS redirection script
Merge pull request #2987 from tractorcow/pulls/2981

FIX Escape the redirect URL before outputting (alternate implementation)
Cast TreeTitle to HTMLText

Closes #2989
Fix link to the HtmlEditorField API page

Closes #2990
Merge branch '3.0' into 3.1

Conflicts:
	model/Versioned.php
	view/SSTemplateParser.php
	view/SSViewer.php
Correct line length
Merge branch '3.0' into 3.1
Correct errors from differening behaviour between 3.0 and 3.1
Correct line length and indentation
Updated translation masters