Improve and simplify Skills Group management

[sudo-may]

On the subject page

• for the skill search also search through all the groups, effectively searching through all skills under a subject
• optional fields control above the skills table should apply to all of the groups

making these changes will allow to remove search and optional fields controls from each expanded group; to accomplish this improvement could change endpoints to simply return all skills under a subject and then arranging skills under groups in the UI code

this will also give us an opportunity to implement additional productivity controls like "expand/collapse all groups"