Description of problem:

Enable only tag categories relevant to the source in the 'Tag Category' dropdown menu on the application details page

In the attached screenshot, when 'Filter by source: Manual' is selected, only the following categories should be enabled : Application Type and Data Center. All the other categories should be disabled.
Similarly, when 'Filter by source: Analysis' is selected, only the categories relevant to source : Analysis should be enabled.

There are two kind of filters for the tags details, the "Source" filter and the "Category" filter, both are complementary from each others.
The Source filter indicate the source of the tags, for instance it contains "Manual" when tags where added manually (when editing the application).
The Category filter contains the categories that are relevant to the tags independently of the source.

we need to go one step further and have the "Tag category" filter to show only the category relevant to the source.
When no "Source" filter is selected then all tag categories used by the current application should be displayed in the "Tag category" filter list.
Conversely if a "Source" filter is applied, then only the tag categories relevant to that source should be displayed (or either have the other categories grayed, as rhn-support-nachandr suggested).