Added

• Added touch support.
  In order to make it work properly on all touch devices, you have to use grapesjs-touch plugin, which just includes some essential polyfills (eg. native drag & drop). Big thanks go to @saltyfoam for funding this feature and @Unsigno who actually made the work. There are still few issues regarding some devices (probably not even related to the feature itself), but we hope to fix them soon