Document permissions and some possible improvements

[Ryan J Ollos]

• The WORK_VIEW, WORK_LOG, and WORK_EDIT permissions should be documented on the project's wiki page.
• If the WORK_LOG permissions does what I think it does, we might rename it to WORK_EDIT, to be more consistent with the permission naming scheme in Trac.
• I've granted WORK_LOG permission to a user, but that user can't start work on a ticket and sees the message WORK_VIEW privileges are required to perform this operation. To be more consistent with Trac implementation of permissions, WORK_LOG (WORK_EDIT) should grant all permissions granted by WORK_VIEW. In the same way, WORK_ADMIN should grant all permissions granted by WORK_LOG (WORK_EDIT).