CONTRIBUTING: Condense info and add directions to other resources

Fixes gh-1824
Build: Remove empty define({}) from build output

Fixes gh-1768
Closes gh-1569
Tests: Update QUnit
Tests: Minor updates for QUnit 1.16 compatibility

More to come later.

(cherry picked from commit f6f8848fbe477fa93fd27ac7f10885dd6e97f633)
Tests: Accommodate page changes from the QUnit HTML reporter

Ref 6748ba349650353c7bed6eec201a3192f6b2cae1
Tests: Tilt at a few style guide windmills

Ref 3c13f4c6297566a71102c2362347987f6d6a636e
Callbacks: Disabling a callback should prevent firing

Thanks to @TheDistantSea for the report!

Fixes gh-1790
Closes gh-1643
Event: Fully clean up events in unit test

Closes gh-1685
Manipulation: improve test for data-URI

Some environments do not support data-uri in "src" attribute of script element.
Mitigate it with equality assertion

Ref a467f8653a6fab2903148df80ab0ce9f5f4fd04f
Attributes: Use the option val hook in select val hook and simplify it

The hook is still defined; not using it could cause issues in IE<11.
Also, IE10 no longer throws when value not set but it still doesn't trim the
value. IE11 has all those issues fixed; support comments are updated.

Fixes gh-1902
Closes gh-1901