Enable customization of TinyMCE init options

[MrCrayon]

tinymce_init_callback and tinymce_setup_callback can only be used effectively to set events or do something after tinyMCE has been initialized, to change init options tinymce currently needs to be initialized, destroyed and reinitialized with new settings.

This PR:

• Exports default settings options
• Moves initialization to rich_text_box blade file
• Checks if custom options are set in BREAD details to merge
• Enables different settings for each textarea
• Adds documentation

Warning
If tinyMCE was used without calling rich_text_box partial it will need to be initialized:

tinymce.init(window.voyagerTinyMCE.getConfig());

Closes #4551

[howdu]

Works well thanks - needed to re-compile via npm due to error:
Cannot read property 'getConfig' of undefined.

I tested by importing extra tinymce plugin into my use of the voyager additional_js importing the extra tinymce plugin there which works well with your changes.

It would be great if tinymce/ace editors were not so tightly coupled into the main voyager app.js file and loaded separately when needed.

[codecov]

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[emptynick]

Couple things:

Lets move the documentation from customization/tinymce.md and merge them together with what you created.
You also need to add a link in summary.md to your new file.

Also it is not very clear to me where I have to put the tinymceOptions.

[MrCrayon]

tinymceOptions go in BREAD details, I should add that.
I'll check the other things too 👍

[MrCrayon]

@emptynick I added a note to upgrade documentation, let me know if that's clear.

[emptynick]

Yep, that's better