RFR: Remove version numbering

[Jesper Wilhelmsson]

Removed release notes and version numbers from all pages. Added a footer which displays file modification date and time
instead. The modification time is currently only placed at the bottom of each file, while the version number was
present both at the top and at the bottom. This was made on purpose. Please leave a comment if you disagree with that
decision. It's a simple makefile change to add it at the top as well.

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Commit messages:
 - Remove version numbering

Changes: https://git.openjdk.java.net/guide/pull/9/files
 Webrev: https://webrevs.openjdk.java.net/guide/9/webrev.00
  Stats: 158 lines in 20 files changed: 5 ins; 152 del; 1 mod
  Patch: https://git.openjdk.java.net/guide/pull/9.diff
  Fetch: git fetch https://git.openjdk.java.net/guide pull/9/head:pull/9

PR: https://git.openjdk.java.net/guide/pull/9