Start loving tablets more.

- Now providing dimension constants for 7" and 10" tablets, for both
  landscape and portrait orientation, for precise control over appearance.
- Fine-tuned the constants for default page margins (and enabled
  dynamically setting the margins in the WebView) for various screen sizes.
- Fine-tuned the font size of the page title and Wikidata description for
  various screen sizes.
- Increased the default text size for large tablets.

Change-Id: I23bb555e59f4756106bae9b14e16c7e11b9f3db4