Completed support for password protected games

![passworded-server](https://f.cloud.github.com/assets/756669/933659/cf45bff0-005a-11e3-93f7-b60d422c912d.png)

I found existing widgets and a dummy password in the handshake request. This makes it configurable. If mod authors dislike this they can just remove the password widget and all servers will be created with blank passwords making this feature therefore completely optional. My personal believe is that passwords are useful if you want private games especially during prime time where kick-banning random people is annoying and mean.

![password-failed](https://f.cloud.github.com/assets/756669/933666/07f27b36-005b-11e3-82a6-9eacff0bfca8.png)

Has been requested in #2290, #3284 and #3367 as well as opposed in https://github.com/OpenRA/OpenRA/issues/2693#issuecomment-14678472.