Brian Steinberg Senior TV EditorMSNBC’s “Morning Joe” will soon become a mid-morning affair when the cable-news outlet expands it to four hours starting April 4.MSNBC plans to air the program from its usual starting point at 6 a.m. until 10 a.m. now, pre-empting a 9 o’clock hour that had previously been earmarked for more traditional news coverage.