update to work with orchardup/postgresql image (which supports postgis)
based a lot on jezdez/dokku-postgres-plugin
Also removed the pre-deploy plugin from kloadut (will re-enable it if it
proves necessary)
cleanup file
remove unused code (VOLUME/persistent data)
update files to take Docker official postgres image
 support for postgis as fork of Docker postgres official image
Merge branch 'postgis-2.1' of https://github.com/mobula/dokku-pg-plugin into postgis-2.1

Conflicts:
	commands
	install