Porting to TinyMCE api v4

[davidemoro]

Convert the plugin code to api v4

[davidemoro]

I've started a porting to api v4 here (wip):

• https://github.com/davidemoro/tinymce_accordion

The main idea is:

• write a generic JS only package publishable on npm, this way it won't be no more Plone specific but reusable in many other framework
• reduce complexity (eg: remove support for select and transform to accordion)
• the package can be optionally included on a Plone's specific package (eg: collective.sweeteditor) using https://github.com/davidemoro/build_commands. This way we decouple the plone package from the JS only generic tinymce plugin
• create a new plugin tinymce_tabs similar to tinymce_accordion.

Probably I won't work anymore on tinymce_accordion but I'd like to help other people interested in completing the api 4 porting. So feel free to contact me if you need any hint.