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.
Skip tags in Zend_Cache for Aggregate if not available

Allows usage of one consistent Zend_Cache backend
for all SilverStripe core storage, greatly simplifying
its configuration. This means a call to Aggregate::flushCache()
will indeed flush all caches if the backend doesn't support tags,
including any custom caches defined through SS_Cache.
Given caches are regarded transient that's an acceptable limitation.
Improved SS_Cache docs, moved to /docs

We keep having trouble with extended PHPDoc formatting,
and have similar topics covered in Markdown already.
Moved docs, added some details about timeouts and
the theory of caching backends.
Merge pull request #2677 from chillu/pulls/zend-aggregate

Skip tags in Zend_Cache for Aggregate if not available, better docs
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.
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
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