Corrects manual installation instructions

The package list contained various invalid package names (which was also the topic of several forum threads already, see e.g. http://forum.owncloud.org/viewtopic.php?f=3&t=3725 or http://forum.owncloud.org/viewtopic.php?f=3&t=2345 .

This should correct the list and the commands, the commands were tested on Ubuntu 12.04 LTS server.