Rework TTY column

* Rename internal identifier from TTY_NR to just TTY
* Unify column header on platforms
* Use devname(3) on BSD derivate to show the actual terminal,
  simplifies current FreeBSD implementation.
* Use 'unsigned long int' as id type, to fit dev_t on Linux.

Only on Solaris the terminal path is not yet resolved.

unsupported/UnsupportedProcessList.c

@@ -54,6 +54,7 @@ void ProcessList_goThroughEntries(ProcessList* super, bool pauseProcessUpdate) {
    proc->pgrp = 0;
    proc->session = 0;
    proc->tty_nr = 0;
+   proc->tty_name = NULL;
    proc->tpgid = 0;
    proc->st_uid = 0;
    proc->processor = 0;