Suggestions for ManageThemes

Changes are for the Manage and Install tab only. Removed some colons, removed <tt> tag (not html 5 compliant), added help button to one h bar, changed some titles to better reflect their section, changed wording in help/boxes to better clarify purpose of Manage and Install section.  Note: The help button on the top two h bars could be removed as that information is redundant and is already contained in the below discussion and information boxes. Just trying to polish it up a little bit, keep what you like and discard the rest.  :)