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 dictionary 'Labels' in web_config.py
• the order of the parameters in the columns follows the order in the 'Labels' dictionary (one can also omit certain parameters from the input files if they are not listed in the 'Labels' dictionary, could be useful for splitting long tables)
• 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, for example when there is an LHCb average)
• allow instances where certain measurements do not measure all parameters in the average (one such example is R_perp in B->D*+D*-), leave them empty
• allow to download multiple output files for uncorrelated averages
• show asymmetric statistical errors
• add separate entries for fit quality of uncorrelated averages

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

• asymmetric systematic uncertainties
• choose significant digits in tables
• fourth error in tables (e.g. model dependent error). I think as of all other systematic uncertainties are summed in quadrature