Updates to the OA code and methods/tool tips + small general edits

[delwen]

• Updated colour scheme of plots on "All UMC" page (EUTT plot now also has same colour for bars)
• OA and Green OA: updated the methods section, methods tool tips, and limitations tool tips
• Updated the intro text on the "All UMC" and "One UMC" pages
• Updated the code of the OA and Green OA plots
  • Different denominator for the Green OA percentage plot and the Green OA absolute number plot