Listofshellcommands

Implementation of a step that runs a list of shell commands in a single step.
All the shell steps share the same env, workdir, usePTY configuration. The tuning of the execution
can be configured by inheriting from that class and overriding methods.
N.B: I did not manage to get rid of the  MISSING BB REFERENCE: bb:step:ListOfShellCommands
error message when generating the doc. I'll keep digging on that issue