Modify vp-comparefits interface

[scarlehoff]

vp-comparefits requires a number of arguments to be added when ran from command-line, however the --help doesn't really help on knowing which they are. I've grouped them so that one can quickly know which are mandatory:

mandatory:
  Mandatory command line arguments

  --title TITLE         The title that will be indexed with the report.
  --author AUTHOR       The author of the report.
  --keywords KEYWORDS [KEYWORDS ...]
                        keywords to index the report with.

Then there're the flags th_covmat_if_present and no-thcovmat_if_present which are both the same one. I guess there might be a good reason why having one of the two was made mandatory but I think it makes more sense to be false by default and use it if needed? I've put as reviewer people who modified this file just in case I broke something important...

Note: I've separated the thcovmat and the groupping commits so I can revert the thcovmat if there's a good reason for making it mandatory.

[Zaharid]

Looks sensible.

[wilsonmr]

Then there're the flags th_covmat_if_present and no-thcovmat_if_present which are both the same one. I guess there might be a good reason why having one of the two was made mandatory but I think it makes more sense to be false by default and use it if needed?

The flag was set to true by default because then it usually does the sensible. thing - uses theory covmat if one was used in the fit and vice versa. The name was supposed to reflect that if there is no theory covmat it still does something sensible* but perhaps it's confusing at the moment considering adding theory covmat is basically unsupported. No strong feeling either way

*absolutely nothing

[scarlehoff]

It might be better then to set it to true by default (i.e., the inverse of what I did, deprecate the thvcovmat instead of the no-thcovmat)? (I'm also fine with both)