PhaROS bridge: users may confuse the use of created subs & pubs

[mcamp]

When users create a sub or pub, the system allows them to use that name in any way. It is necessary to give some signal to the user that, a pub variable, can not be as a sub.
For example:

{pub -> 'some_topic'}
(machine bar
(state foo
(onentry [robot pub]) ;; this is an error, pub does not exist as a getter, only as a 'setter'
)
)

We should mark this kind of errors