This fixes up a couple of long-standing issues in the repository

configuration page. The first and most major is a fix to prevent the

browser from trying to auto-fill the username and password fields for a

repository with the user's own credentials, which is almost never going

to be correct. Browsers try very hard to do this if they see anything

that remotely looks like a password field, and while we attempted to

combat that in the past, browsers have gotten smarter.
The better trick, which has worked on RBCommons for a long while, has

been to create a password field higher up on the page that is visible

but located far off-screen, and doesn't contain a form field name so it

won't be sent to the server. This takes care of the issue on all major

browsers.
The other fix is for the "Use hosting service's bug tracker" checkbox,

which was showing up for hosting services that didn't include bug

tracker support. It was greyed out, but its presence was still

confusing. We now hide that checkbox's row entirely.

Tested the page on Chrome and Firefox. The browser was no longer

filling in the password.
Tested the bug tracker checkbox for all supported hosting services,

making sure it was only present when it could be enabled.