support for fully qualified domain names not just subdomains

Currently dokku is limited to subdomains of the `$HOME/VHOST`. This PR adds support for fully qualified domain names.

If the `$APP` contains a `.` character in it, then it will be treated as a full domain name, if not it will retain the old behaviour which is to be a subdomain of the `$HOME/VHOST`.

For example:

```
# pushes to blah.eugeneware.com
$ git remote add dokkufull git@myserver.com:blah.eugeneware.com
$ git push dokkufull master
```

or:

```
# pushes to blah.myserver.com (as myserver.com is the VHOST)
$ git remote add dokkusubdomain git@myserver.com:blah
$ git push dokkusubdomain master
```