Added optional port fields to database configuration forms.

As per #36, adds a `db_port` input for the user to specify a non-default port for the various database configurations. 

I just threw together an initial implementation. I wasn't sure about a couple things, so I figured I'd throw them up here for consideration: 
* Using `input[type=number]` - Not sure what the target compatibility is or what the issues would possibly be with using this. I can't imagine people using modern web frameworks and systems using anything too old to support this. Some style changes would be necessary to make those stupid increment/decrement buttons look nice... in my opinion, anyways.
* Not showing these fields by default for cleanliness? I considered having them hidden and having something the user clicks to reveal the field just to keep the form's simplicity by default. 
* Removing the `db_port` field altogether and allow the `host:port` notation in the `db_host` field and informing the user of this option in the help text beneath the field.