Landing page updates

• from pr #551
• commits from: @dougoldenburg, @lheagy
• review from: @lheagy

Updates to the landing page

• Altered "What is EM Geosci"
• Added "EM Geosci and the SEG" with the SEG logo
• Altered the "Under Construction" only by changing the date.

DC: Image sizes on sounding app

• from pr #530
• rewrite html radio button widget for the DC resistivity sounding curve as noted in #529 so that the images are large enough to be visible.

Improve description of apps

• from pr #528
• commits from: @lheagy
• review from: @sgkang

First impressions

• add the case history image to the index page
  

Apps

• more description on how to get up and running with Binder, Azure
  

General cleanup

• update copyright year to 2018
• bibtex cleanup
• add live links that are slow to resolve to the linkcheck ignore
• add versioning info to the site, including links to release notes for the changes with each version

EM GeoSci Initial Release

Version of EM GeoSci used in the 2017 Society of Exploration Geophysics Distinguished Instructor Short Course entitled Geophysical Electromagnetics: Fundamentals and Applications (DISC 2017) taught by Doug Oldenburg (@dougoldenburg ) with Seogi Kang (@sgkang) and Lindsey Heagy (@lheagy) as co-presenters.