Add support for multiple destinations

[Lyalpha]

To help IO balance things, it would be benefitial to send part of the raw data to separate storage disks.

This would be enabled by passing multiple valus of destination and pattern arguments, which must both have the same length. As an example:

raw-transfer /data/goto/images --destination user@host1:data1/raw,user@host2:/data2/raw \
                 --pattern "t[1,3]_r*_ut*.fits", "t[2,4]_r*_ut*.fits" 

would transfer t1_ and t3_ files to /data1/... on host1, with t2_ and t4_ files going to /data2/... on host2