Require login for all pages in Munin Admin

Because we would like to have Munin Admin secure, we should default didn't allow any usage without login. In the mibe image we already create an valid admin user who is able to login.
Add HTML templates for login and password change
Update and modify url routing
Add login URLs into template
Merge pull request #2 from drscream/master

Login should be required to use the Munin Master Admin interface