Added Webcord, office apps, and some scientific computing apps

[GabePoel]

Added icon for Webcord based on the existing Discord and Discord Canary icons. Also added Mathematica, Octave, Okular, and a bunch of Microsoft Office/Google Suite apps. Note that I haven't added symbolic versions of all the app icons. I also put in mimetypes for everything.

[somepaulo]

Thanks for this huge commit.

I can't accept all of the proposed icons.
Office file mimes (documents, spreadsheets, presentations, html files) are already being taken care of by Adwaita, which we don't interfere with, and there's no point differentiating their icons for one particular office suite. If these particular mimes you've included don't get covered by Adwaita for some reason, what we can do is include Adwaita's original icons for them and create symlinks to them with the needed filenames.

So if you don't mind, I'll cherry pick from this commit.

[iaacornus]

hi can you make a merge request of this in the revived repo MoreWaita-Dev/MoreWaita? Thank you!

[iaacornus]

hi, i'll be absorbing this in my repo. Thank you for this nice contribution @GabePoel