v0.18.3

Feature:

• updated tinymce to 4.9.11
• updated tinymce integration so to be able to upgrade to newer tinymce releases (we stuck to 4.5.x because of tinymce issues): core should be now compatibile with 5.x (and maybe 6.x) releases too (#644)

Fix:

• make scrollIntoView less prone to exceptions

Developer notes:

• extracted editing widgets to their own files in form of widget plugins
• added experimental Url.templatePath and Url.imageProcessor methods for the templating language (NOTE: the code was published here, but included in runtime only after 0.18.5)