Initial support for custom PressBooks markup buttons in TinyMCE (ticket #748).
Web chapter number styling fix to match the rest of theme for Luther, Clarke and Donham.

Ticket #789

Signed-off-by: Sonia <sonia@nudge.ca>
Custom markup buttons in TinyMCE

Moved metadataManagerDefaultEditorArgs to Editor class.
Repositioned dropdown to second row, third row looked weird and did not toggle with kitchen sink.
Repositioned footnote buttons to second row.
Renamed class methods to camelCase, prefixed functions with static, coding standards.
My IDE auto-formated some stuff, changed some tabs? File under coding standards.
MOBI Validation Error: Cover is too small

Reduce amount of "Cover is too small" errors we see in the logs from kindlegen.

* Ideal height/width ration of 1.6
* A minimum of 625 pixels on the shortest side and 1000 pixels on the longest side
* For best quality, your image would be 1563 pixels on the shortest side and 2500 pixels on the longest side

@see: https://kdp.amazon.com/self-publishing/help?topicId=A2J0TRG6OPX0VM
Check if image is actually an image

Sometimes due to user error he/she will point to a GIF, JPG, PNG that returns a 404, webpage, or text.
We don't want to include this in an Ebook.
Revert back to old global $id, if any.
chmod 664 functions.php

This file should not be executable.
Make transformXml() more robust
Freebie toggle
Tag broken images with #fixme
Added MCE stylesheet for previewing custom styles.