Select images on mousedown using Rangy

Removes _selectedImage.
Add test for unlinking image.
TridentPre7's _keyup: remove unused assignment
Image selection test.
Image selection test: assert only one node selected
Use `manipulationFunc` in image selection test
Merge branch 'classToggling' into selectImagesWithRangy

Conflicts:
	src/test/unit/specific_feature_tests/images.js
	src/wymeditor/editor/base.js
Make JSHint happy.
Merge branch 'master' into selectImagesWithRangy

Conflicts:
	src/wymeditor/editor/base.js
`editor.getSelectedImage` including api doc and tests
Fix toggleClass
Use IMG_SRC in a few places in tests
_selectSingleNode
Merge branch 'image-dialog-focus-before-insert' into selectImagesWithRangy
Merge branch 'qunit-hide-passed' into selectImagesWithRangy
_selectSingleNode: return statement is supposed to be throw
Fix image dragging and dropping
Docstring for _selectSingleNode
Tests with image selection: skip in PhantomJS
Make JSHint happy