Add openTeletype option for use without shell

An external developer might want to open a teletype in a Session or a Part without an additional shell interfering / in background (e.g. pty to /bin/vi). Therefore, a new optional argument is introduced to run a pty process standalone. Consistency is held with legacy method calls.

Beside adding the new optional argument for openTeletype(), the change that has to be made to actually stop the shell from running is in Session.cpp. There, the Session constructor calls openTeletype() to create the _shellProcess, but more important that method adds a callback from end of initialization of _emulation to Konsole::Session::run. Given the case that teletype needs to be used without the shell, this is what needs to be prevented. However, using Konsole as a Part, the external developer has no direct control over the constructor of a Session - as such the mentioned callback needs to be removed if the user wishes not to run the Session.

This is essential for running an interactive application like /bin/vi correctly (old: both, sh and vi interpret inputs and write ouput, simultaneously) via teletype in a Konsole Part. One may compare the old and the new behaviour of PartTest.cpp, where there is no shell prompt cluttering the output anymore. The old behaviour is kept as default.