RFR: JDK-8287674: CSS improvements for summary lists

[Hannes Wallnöfer]

This is a refinement of CSS styles mostly in the deprecated and new API pages.

 - Provide a two-row table view for the new sortable three-column tables
 - Make sure no line wraps are inserted between a checkbox and its label
 - Slightly increase the line height of the check box row to make it easier to use when wrapped
 - Define the overflow of summary table cells as "auto" which makes them scrollable if necessary

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Depends on: https://git.openjdk.java.net/jdk/pull/8973

Commit messages:
 - JDK-8287674: CSS improvements for summary lists

Changes: https://git.openjdk.java.net/jdk/pull/8975/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8975&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8287674
  Stats: 36 lines in 5 files changed: 16 ins; 4 del; 16 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8975.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8975/head:pull/8975

PR: https://git.openjdk.java.net/jdk/pull/8975