Add Export Scores feature

[dens0ne]

I ran a league with a friend of mine and he asked me if there was a way to keep track of match scores locally, and I thought it would be a good idea to have that. So here it is:

• Added a button to the Score UI to "Export Scores"
• Added method to export scores in XLSX file (output goes to /out/score_export.xlsx)

Additionally, added a Contributing MD file for anyone who may want to contribute into the project and don't know how to get started. This would fix an issue I opened some months ago: #913

Screenshots:

Scoreboard with button and modal after exporting scores

Export file

[ZombieHDGaming]

Hi!
Thanks for the contribution. Before this PR goes anywhere, just for clarity sake, what does this export look to accomplish? I understand that it keeps a running local export of matches and scores, but I want to try and see if there's use for such a feature outside of just that, as it may need to be tweaked a bit implementation wise before it would go into TSH itself.

[dens0ne]

what does this export look to accomplish? I understand that it keeps a running local export of matches and scores, but I want to try and see if there's use for such a feature outside of just that, as it may need to be tweaked a bit implementation wise before it would go into TSH itself.

Hello!
Just keeping track of matches scores. We had to maintain a file manually separately and it is a bit annoying. I don't have any other use case in mind at the moment