Split "bind" and "port" into separate webserver config values

[ARolek]

Currently our webserver config takes in a port which is actually an "address" (i.e. "0.0.0.0:8080" or ":8080"). Our PostGIS provider takes in the port as an integer. In an effort to keep things consistent, the webserver should require the port to be an integer and allow the user to provide a bind value.

[JivanAmara]

Related to #210

[JivanAmara]

Note to self, looking more closely at the config processing should shed some light on: https://github.com/terranodo/tegola/blob/issue-161_geopackage_provider/provider/gpkg/gpkgProvider.go#L379

[gdey]

#545 When we do this we should, also, consider #545. We need a way to prefix our generated urls with a prefix.