Added the 2mass-band option to mHdr.

[catherine-martlin]

Hello, @astrofrog! I need the MAGZP keywords in the header of my 2mass images for a pipeline I am working on - the original Montage command mHdr allows that by using the keyword -t. I saw that issue #52 had been opened but not yet dealt with. I added the optional keyword with description to the proper function in montage_wrapper/commands.py. Is there anything else I would need to do? Is it possible to have this reviewed and merged into the package?

[catherine-martlin]

@astrofrog - I was hoping to get a status update on this PR? This is certainly low priority as it's likely out of date and Montage has their own Python wrapper now, but that version doesn't include the mExec command which I also need for my pipeline so I was hoping this update could be incorporated to ensure my documentation for my pipeline is slightly more simple than having to send future users to my specific branch of this wrapper. Thanks!