Use the first configured credentials when there is only one.

This will avoid to ask for the github.com credentials when the only configuration is related to enterprise.
Remove the scheme from the project host before creating the project's git url.

When the host is absolute, like https://github.enterprise.com, the creation fail because the git url is malformed, like:

git@https://github.enterprise.com:foo/bar
Allow to configure enterprise urls with and without scheme.

Letting decide to the user because we don't know which one they are using, using https by default.
Check the available hosts and credentials before asking for them for the default host.
Allow to select host when the configuration includes more than one credential.
In GitHub.apiEndpoint, refactor to get host and return an absolute URL
Make knowHosts and defaultHost private
Tag remove CurrentProject
Merge branch 'calavera-credentials_improvements'