Add presentation materials, unlinked

[nchan0154]

I had some time today so I scoured the backlogs of the email archive for as many presentation materials as I could dig up. I am certain there are some missing as @prushforth and other members of the team may have received some directly, so feel free to edit this PR and post as required.

I updated the templates so they would display recordings like so, where the title is a link to the recording and '(slides)' is a link to the slides

I have added, but not linked, slides from:

• Brandon Biggs
• Sebastian Felix Zappe and Holger Dieteric
• Claudia Loitsch and Julian Striegl
• Me!

I found slides to, but have not linked as they were not downloadable/too large to contain in this Repo:

• Brian Kardell: https://slides.com/briankardell/deck-c653bb
• Brandon Liu: http://bdon.org/maps-for-the-web/

I have found the following recordings for @tguild to upload to the official youtube channel:

• Nicolò Carpignoli, Towards accessible annotations for a native map viewer for the web platform user needs and requirements: https://www.youtube.com/watch?v=nsPkfKSkSj0&feature=youtu.be&ab_channel=Nicol%C3%B2Carpignoli
• Gobe Hobona, OGC Standards for API Web Use https://portal.ogc.org/files/?artifact_id=94865
• Claudia Loitsch, Julian Striegl, Accessible Indoor Maps: https://cloudstore.zih.tu-dresden.de/index.php/s/Z5SfoojCfLCwdLq
• Nic Chan, UI patterns in existing web map widgets https://www.dropbox.com/home/maps4htmltalk/talk-export

[prushforth]

This is awesome Nic, thanks a lot! I just received Dan Little's presentation, possibly for the second time, and I'll attempt to follow your lead example for that. I have just been madly trying to finish my own presentations, which have ended up being a much bigger job than I anticipated (I should have known).