Change basic data structure to astropy.table.Table

This requires chagnes in almost all modules. While looking through the code at all places anyway, I shrtened other stuff and tried to make everything more general, so that it works with more bands. Only the plot stuff is still hardcoded to IRAC1 and IRAC2.
Merge pull request #7 from YSOVAR/astropytab

Change basic data structure to astropy.table.Table