[11] Review request: 8201261: Ability to override the dependency repositories used by gradle

[Kevin Rushforth]

Phil,

Please review the following:
https://bugs.openjdk.java.net/browse/JDK-8201261
http://cr.openjdk.java.net/~kcr/8201261/webrev.00/

This adds support for two new gradle properties, JFX_DEPS_URL and 
JDK_DOCS_LINK, replacing logic currently in the closed build. Details 
are in JBS.

-- Kevin