Abstract Ubuntu dependencies into scripts

I moved the dependencies into separate install scripts to make it easier to get started. The scripts contain the differences between 11.04 and 12.04 (the thing with libxcb-icccm1-dev and libxcb-icccm4-dev) and all common dependencies are placed into install-deps-common.sh

This is also good when something changes, we only need to update the install scripts and we also have a clean separation between 11.04 and 12.04 in case anything else changes. Also, if another environment is supported we can just add another dependency script and don't have to update the README