Since register and unregister cant be used without full zmq initialization,
it should make sense to also check flag for them.

Checking was done inside of emit method. Doing on emit function at
a module level makes it cleaner with less lines inside of check.

Change EventsClientThread behavior so it won't start anymore if
the events flag is set to False

this will be used to allow the unittests to disable the events
framework. this way, emit() will become a passthrough.

note that, until now, the basetest class is making use of the threaded
version of the client, which launches a zmq tornado-based ioloop. this
is wrong, and will have to be addressed in a future commit. we'll have
to make use of the global EVENTS_ENABLED flag in the txclient version
when those changes are made.

Related: #7259
Relases: 0.4.2

this, together with the events server registration, was breaking the
events signalling on the client whenever it used ipc:// sockets.

the idea is that we'll be able to use the threaded version of the
client, which makes use of the tornado ioloop, in a non-twisted module,
like the main graphical client probably will be in the near future.

The emission of an event was being logged twice, and the second time was
logging the pickled content of the event. This pickled content contained line
breaks and other things that caused strange output on the client log.

This commit removes the second loggin of the event pickled content.

Closes #7130.

previous regex wasn't capturing addresses of type ipc://<path>

Closes: #7089