Add Case Subject and modify UI

As posted on the forum (http://forum.civicrm.org/index.php?topic=14947), it'll be good to have a Case Subject to make cases easier to identify at a glance.

Suggestions are:

• insert the subject into the "subject" field in the case table (so it becomes both a Case subject and a Open Case activity subject)
• show the Case subject on the Dashboard pages, preferably between the Client and Status
• in the Case Summary, merge Case Type and Status in the same way the contact and phone number currently is, and insert a new column for Case Subject after the Case Type/Status column