Backwards compatibility for package name changes

[5iver]

This PR includes:

• Support for the package name changes that occurred due to the ESH reintegration into OHC. I did my best to also prepare for future package name changes that will occur in the OH3 release. (fixes Errors on startup after upgrading to build 1522 #82)
• Fix for StartupTrigger and other custom handlers (fixes Missing handler error when using custom TriggerHandlers #44)
• Removed ShutdownTrigger, as this is not functional
• Jython 2.7.1 and 2.7.2 compatibility (fixes Problem with helpers and Jython 2.7.1 #28)
• Added check in core.init to only add the Item attributes to items if Items already exist (fixes Error during loading of 'core/000_startup_delay.py' at startup #54)
• Some other minor cleanup
• Fixes in core.items and core.links (that were meant to go into [items] Add ManagedItemProvider #111 ☹️)

Signed-off-by: Scott Rushworth openhab@5iver.com