fixed wrong url path to icons sprite

one url() call to the sprite img was wrong. fixed it like the other paths.
Merge pull request #31 from piffie/patch-1

fixed wrong url path to icons sprite
Correct options.history assignment when options.enabledHistory used.
Merge pull request #33 from vbortone/hotfix/1.7.0.1

Correct options.history assignment when options.enabledHistory used.
Merged v2.0.0
Merge branch 'develop'
Updated readme
Updated tile for chrome web store
Added placeholder file for the beta version
Fixed undefined variable editor in _onRedo
Merge branch 'master' into develop