Update new site to include remaining gerritcodereview.com pages.

Changes include:

* Moved the about page out of gitiles and into the Jekyll site. Update the
navigation (top and sidebar) to include new file. Retitle file "Gerrit's
History."

* Moved issues page into Jekyll. Update top navigation. (this file is not
needed in the left nav)

* Moved releases folder

* Moved "docs" folder. (Is this folder still necessary?)

* Deleted:
  * foo.md (test file)
  * googlebdbd1417c92a607.html (an attempt to show ownership of site)
  * Gemfile (not needed because Docker)
  * Gemfile.lock (not needed because Docker)
  * images directory (copied into jekyll-source folder earlier)
  * index.md (outdated)
  * navbar.md (obsolete)
  * firebase-debug.log (unintentionally added)

Change-Id: I6829109ebfef05183a614c0b5621fcab2b5b9fa1