Initial test files creation
Add unit tests for hover preview
Adding image files used in unit tests
test popover positioning
Merge branch 'master' into rlim/hover-preview-unit-tests

Conflicts:
	src/extensions/default/HoverPreview/main.js
Export all hover preview functions as private functions to unit tests.
Update test file with some repeating-linear-gradients, repeating-radial-gradients, and some invalid color names.
Update unit tests with the correct cursor positions for all unit tests.
Merge pull request #3475 from adobe/rlim/hover-preview-unit-tests

Adding hover preview unit tests