Greek letters and minor improvements of special char

[AndiU]

Hi,

I added greek letter to the special character plugin, as in scientific environments these are needed on a daily base. They were already defined in ​http://docs.cksource.com/ckeditor_api/symbols/src/plugins_entities_plugin.js.html in order to allow them to insert, but the special char plugin didn´t offer them.

As greek and also latin letter(!) can be disabled, I made the inclusion optional. Also I added the following missing characters to special chars: "Š","š","Ÿ"

Language file is also updated.

Please the the files attached

[AndiU]

specialchar/plugin.js

[AndiU]

specialchar/lang/en.js

[Garry Yao]

@AndiU, thanks for the patch, the default special char plugin is just providing an scaffold for extending with your own customization, the editor doesn't have to ship with everything.