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.
more docs for GridField & ModelAdmin customization
Merge pull request #2959 from Zauberfisch/patch-4

Improvements on GridField customisation docs
HtmlEditorConfig default TinyMCE mode is now none
Merge pull request #2297 from colymba/htmleditorconfig-mode-fix

HtmlEditorConfig default TinyMCE mode is now none
NEW Added FormatFromSettings(). Formats dates as per user preferences.

- Required for silverstripe-cms/issue/965.
- Separate implementations for Date and SS_Datetime.
Merge pull request #2961 from phptek/cms-issue-965

NEW Added FormatFromSettings(). Formats dates as per user preferences.
Allow DB::connect() to specify the connection name.
Close the mysqli connection when deleting the class.
API Polymorphic has_one behaviour
Merge pull request #2206 from tractorcow/3.2-polymorphic-relations

API Polymorphic has_one behaviour
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
typo fix

upated should be spelled updated
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