Draft: web_devs updates

@mkenzie @jobutter I added a few modifications to the website scripts and a few more entries of the beta averages using the new plotting utilities. The changes can be seen at: https://hflav-eos.web.cern.ch/hflav-eos/triangle/web-devs

Changes to the web devs:

• adding latex labels for the column parameters with a dictionary in web_config.py
• allow to select which entries of the input files to list in the tables rows (sometimes not all the entries of the input file are use for the averages)
• allow instances where certain measurements do not measure all parameters in the average (one such example is R_perp in B->D*+D*-)
• allow tables for single measurements without average

Other things which I haven't added yet but I think would be useful to have:

• choose the order of the parameters in the columns (right now it follows the order in which they are written in the input files)
• allow more than one table per subsection, see for example the case in the screenshot below, where different observables were measured for the same mode