RFR: 8267551: Support loading images from inline data-URIs

[Michael Strauß]

This PR adds support for loading images from [inline data URIs](https://en.wikipedia.org/wiki/Data_URI_scheme), which is also widely supported by web browsers. This enables developers to package small images in CSS files, rather than separately deploying the images alongside the CSS file.

-------------

Commit messages:
 - Added data-URI loading support for images

Changes: https://git.openjdk.java.net/jfx/pull/508/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=508&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8267551
  Stats: 437 lines in 8 files changed: 414 ins; 9 del; 14 mod
  Patch: https://git.openjdk.java.net/jfx/pull/508.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/508/head:pull/508

PR: https://git.openjdk.java.net/jfx/pull/508