RepositoryForm contains a couple of variables used for form storage,

which is specific to forms created by hosting services. These are called

repository_forms and bug_tracker_forms. Those names indicate that

these are general-purpose form storage dictionaries, which is confusing

since they are in fact structured to tie directly to hosting services.
As a small cleanup, and preparation to be able to have similar forms

owned by SCMTools directly, this renames these variables to have a

hosting_ prefix.
The templates and JavaScript have also been updated to ensure these

entries are properly namespaced, in order to avoid possible collisions

with SCMTools.

Unit tests pass.
Tested every hosting service and bug tracker, ensuring that the right

fields appeared for the selected entries, and that the right state was

saved when saving the form.
Tested that validation and error display of subforms was still working

correctly.
Tested that the hosting service and SCMTool info dictionaries in the

template were still populated.
Tested configuring no bug tracker, a custom bug tracker URL, a bug

tracker using a custom hosting configuration, and a bug tracker using

the repository's hosting service.