This updates the configforms typing code and unit tests to fix some

typing issues that were encountered. These consisted of missing imports,

undeclared member variables/attributes, model attributes that weren't

marked as optional, and undeclared prototype attributes.
There's also a fix to tsconfig.json, which was causing Backbone

types to fail to be looked up. We now use the same setting that we have

in Review Board.
There were also some legacy String.strip() calls (which Djblets injects)

that have been converted to native String.trim() calls.

Verified that no typing issues remained.
All unit tests pass.