Add support for HTTP users / do not force users to have SSH keys

[syphernl]

It appears that this plugin only works with SSH Pubkeys. If I do not add one, the "redmine_dummy_key" is being added while otherwise its a redmine_username_xxx_xxx value.

There does not appear to be a way to simply add the username and deal with the handling somewhere else, in my case this is nginx where the username is just that.

[n-rodriguez]

Gitolite works with SSH keys... I don't see how I can bypass this...

[n-rodriguez]

Actually you were right... This should be possible...