Modify Advanced Search UI

The form no longer always displays an unusable blank field group. It was 
creating user confusion. However, a (usable) blank field group is 
displayed if no existing parameters were present on initial page load.

In the process, much of AdvancedSearchRows was re-written. Reviewing the 
change may be easiest by reading the as-currently-is file rather than 
trying to grok the diff.

There was one incidental behavior change: upon adding another field, any 
existing field is frozen at its current type. This prevents a user from 
getting into a scenario where two fields of the same type are present.