Changed Enumerations to use a Single Table Inheritance

Changed Enumerations to use a Single Table Inheritance

* Added migrations to change Enumerations to an STI relationship
* Added TimeEntryActivity model (STI)
* Added DocumentCategory model (STI)
* Added IssuePriority model (STI)
* Added Enumeration#get_subclasses to get a list of the subclasses of Enumeration
* Changed Enumeration to use the STI type field instead of the opt field
* Changed Enumeration#opt to return the old opt values but with a deprecation warning.
* Removed Enumeration::OPTIONS
* Removed the dynamic named_scopes in favor of specific named_scopes.  Kept for
  compatibility reasons.
* Added Enumeration#default so each subclass can easily find it's default record.
* Fixed Enumeration#default to use the STI scoping with a fake default scope for finding Enumeration's default.
* Added a 'all' named scope for getting all records in order by position.
* Added Deprecation warnings to the old named_scopes in Enumerations.
* Moved various methods off of Enumeration and onto the concrete classes
* Changed the EnumerationsController to use types
* Updated the Enumeration list template
* Added has_many relationships to the Enumeration STI classes.
* Fixes for tests.

  #3007

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@2777 e93f8b46-1217-0410-a6f0-8f06a7374b81