Additional post-installation messages [tracker 32216]

Adds the following post-installation messages:
- Welcome to Joomla!, for new installations only (do not add message with ID 1 to the com_admin/sql files!)
- Secure (bCrypt) password storage, if this feature is disabled in the User - Joomla plugin

Ref tracker item 32216 http://joomlacode.org/gf/project/joomla/tracker/?action=TrackerItemEdit&tracker_item_id=32216&start=0