client commands refactoring  (op/deop/msg done, leave wip)
refactoring to simplify client command parsing
every command now follow the refactoring
comments
refactoring: rename users/:uid/msg/ route to server/users/:uid/pending/
doc for pending messages route
add postCommand (will replace postToChannel) and refactoring of pfc.leave(...)
adapt the join command to the commands refactoring