Fixing issues where the user has multiple connections

[StanleyGoldman]

• This pull request depends on Disabling Release Lock when appropriate #968 being merged to master

Fixes #967

• Authenticating with a token to GitHub Enterprise would result in the scheme and host address being stored in the keychain's host field. Whereas authenticating to GitHub would store only the host. The fix is to only store the host address as expected.
• Getting the current username based off the keychain of the current repository's host, if such a keychain entry exists. If it exists and the username matches, allow the user to "Relase Lock", otherwise that option should be disabled or not visible.

[shana]

I get it :)