Extensive update

• Incorporated previously designed but unreleased table-calculator option in order toallow Excel spreadsheets or CSV files to calculate NPM scores in bulk
• Updated appearance to match HASP branding
• Individual product calculator - functionality identical, but have updated appearance to make more high-contrast and match HASP branding
• Extensive updates to user guide, adding in reference tables, documentation for bulk-product functionality
• Update to citation and references in "About" page

Full Changelog: https://github.com/Leeds-CDRC/NPM-Calculator/compare/v1.1...v2.0.0-beta