Merge pull request cornerstonejs#312 from dannyrb/master

fix: making it easier to listen for the ELEMENT_ENABLED event

feat(uuid): Added a global UUID to cornerstone enabled elements to al…

…low for easy tracking of elements from other libraries (e.g. cornerstoneTools). (cornerstonejs#310)

Version 2.2.4

Version 2.2.3

Version 2.2.2

Create release version 2.2.1 (cornerstonejs#266)

Version 2.2.0