Include cache_suffix tinymce parameter in project's static files

[Pantzan]

This PR aims to integrate Tinymce's cache_suffix parameter into Django-tinymce.

The problem: In project deployments it is a common practice to cache static data for long period of time in both proxy (such as Nginx) and browser storage. When a new version of tinymce or django-tinymce is deployed browser cache cannot be cleared on Nginx request. Tinymce includes the cache_suffix setting to solve this problem by appending a url parameter as suffix, for example ?ver=6.8 in each file in order to force the browser to refetch the static files. When the setting is set in TINYMCE_DEFAULT_CONFIG the suffix is not propagated in the compressor nor the init_tinymce static files.

I believe it is useful feature to be included in this project. Dealing with broken forms is a headache after a new release.

If you have any questions or you would like to discuss it further, I will be happy to participate