State of a project - ability to disable projects

I suggest to introduce states of the projects: active, disabled and archived

• disabled: the project remains on the same "project list" as the
  active project (the continuum homepage), but the project links are
  greyed out. Continuum will not check for modifications. Projects can
  be enabled again to become active.

With this states, someone could write a program that disables a
project if no commits were done in the last x weeks and archives a
project if no commits were done in the last x months. Also, if a
commit is done in a disabled project then the project could be enabled
again.

(This issue was split into two - see CONTINUUM-2099 for the ability to archive a project.)