RFR: JDK-8248566: Make API docs more usable on mobile browsers

[Hannes Wallnöfer]

The purpose of this change is to make javadoc generated pages more usable on devices with smaller screens such as phones and tablets. Changes are mostly in `stylesheet.css` along with a few small changes in generated HTML pages.

 - A `viewport` meta tag is added to every page to tell browsers that the page is optimized for small screens and shouldn't be rendered using desktop dimensions and scaled down to actual browser size.
 - The right-floating `about-language` element is moved forward before the list of main navigation links, and the display style of that list is changed to `block`. This allows the navigation links to wrap around the `about-language` div when space gets tight. Also, navigation `height` entries are changed to `min-height` so they can grow when broken to more than one line.
 - Media queries are added to slightly shrink various page components for smaller browser widths. This includes the search input, navigation bar fonts and various spacings within the page. 

API docs rendered with this change can be viewed here (overview and java.base module pages only):

http://cr.openjdk.java.net/~hannesw/8248566/api.02/

The page should look the same as before the change when viewed in a normal-sized desktop browser. The changes should be visible when resizing the browser window, viewing the page with a mobile browser emulator (available in developer tools of various desktop browsers) or viewing the page on a mobile device.

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Commit messages:
 - Merge openjdk master
 - Tweak styles to minimize changes in desktop view
 - JDK-8248566 Add styles for mobile browsers

Changes: https://git.openjdk.java.net/jdk/pull/1008/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=1008&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8248566
  Stats: 81 lines in 4 files changed: 70 ins; 6 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1008.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1008/head:pull/1008

PR: https://git.openjdk.java.net/jdk/pull/1008