Preparing the gem for release; adding project-scoped blocks from other plugins

Following the guidelines in https://www.openproject.org/projects/openproject/wiki/Developing_Plugins,
the gem was prepared for release

  * added copyright-headers
  * added readme
  * gemspec extended

This also fixes an issue with plugins, that want to add views for the
my_project_page: The mechanism now looks for blocks in the
my_projects_overviews-folder of the plugin and adds them to the
configuration using the document's name (Very similar to the way my_page
does this in core.) An example for this can be found in the
documents-plugin, which now provides views that either show all
documents the user can see (in my/_documents.html.erb) and scoped to the
given project (under my_projects_overviews/_project_documents.html.erb)
minor fixes (removed a debugging-statement, added a ticket-number to the changelog)
Merge pull request #10 from finnlabs/feature/rails3_prepare_for_gem_release

Feature/rails3 prepare for gem release