initial push for ss3ification
progress on ss3 upgrade. tree loading in via ajax, form saving and adding connectors, added minor css and js sparkles.
merged conflicts
import form working in ss3
added custom tree icon css for content sources and items
bugfix made CacheService::inst() a static method
bugfix store children of source as private var not static
Disabled defunct modeladmin-based external content importer (although I agree that a ModelAdmin-based one is the way to go)
BUG Add form reference to the new fields.

This fixes the problem with the CMS linking popup crashing.
TreeDropdownField template calls FormField::Link which in turn requires
a current form reference.
Replace deprecated function call.
Disable the linking form - javascript loading problem.

Prevents the linking form from being visible at all.
Merge pull request #1 from mateusz/linking-form-fixes

Linking form fixes
FIX: Removed crazy bugs in panel reloading due to a misplaced cms-tabset class.
FIX: Fixed subtree loading in external content admin.
Merge pull request #3 from sminnee/ss3

SS3 support, by Shea, Mateusz, and Sam
Updated version information for SS 3.0 release
Added composer config for the 3.x-compatible version.
Updated doco to point to ss24 release
Merge pull request #5 from sminnee/composer

Added composer config for the 3.x-compatible version.
Relaxed version constraint, as it excludes master