Update control file naming system

[wknoben]

Currently we have:

• Control files per domain, and ...
• A script in 1_folder_prep/ in which we specify the control file we want to use, which ...
• Then copies the contents of the domain control file into control_active.txt, which ...
• In turn is what every other script looks for.

Cleaner would be:

• Control files per domain, and ...
• A single line in control_active.txt that specifies which domain control file to read, so that ...
• All other scripts simply read which domain control file has the info they need, pretty much as if the correct control file were specified as a command line argument.