Added project module concept. A project module (eg. issue tracking, news, wiki,...) is a set of permissions that can enabled/disabled at project level. For each project, modules can be enabled on the project settings view ('Modules' tab). This requires a specific permission: 'Select project modules' (if this permission is turned off, only Redmine administrators can choose which modules a project uses). When applying this migration, all modules are enabled for all existing projects. git-svn-id: http://redmine.rubyforge.org/svn/trunk@725 e93f8b46-1217-0410-a6f0-8f06a7374b81