various fixes for "Alter a quota" screen

1. The title should be "Manage quota"
2. The two tables on this screen should be labeled as "current" and "history"
3. The form label "Quota to add" should be "Amount to alter quota (add or decrease)"
4. The form should be at the top of the page in a fieldset - open if there is no history for the user

(marked critical since I see this as a pre-6.x-1.0 feature)