Adding ability to specify frame data types by IFO

Now you can add the following in config ini files

[General]
frame_data_types = {"H1" : "H1_HOFT_C00",
                    "L1" : "L1_HOFT_C00",
                    "V1" : "V1Online"}

The above example is actually the default, and can be omitted. Any IFO and data type can be specified.

Note that I explicitly chose to use JSON formatting instead of following the alternative format

frame_data_types = [H1=H1_HOFT_C00,L1=L1_HOFT_C00,V1=V1Online]

as it is not a standard format, and is parsed by a fragile function that relies on eval.