#2 Add additional commands to before/after starting a pr

[Kyrre Begnum]

One should be able to define some commands one wants to
execute before the VMs are started. This block should be specified
in the global block.

There is some question if these commands should be run if only a
single host is addressed by mln. i.e

mln start -p test -h one

Would this apply for running the project-commands over again?

Also, the upgrade has no real framework in order to check if this
block has changed. This need to be added aswell.