Add WYSIWYG toolbar to WordCamp Spreadsheets plugin

[iandunn]

The WordCamp Spreadsheets plugin uses SpreadJS to embed an editable spreadsheet inside a custom post type.

It needs a WYSiWYG toolbar to so users have a friendly UI to format text, sort data, etc. SpreadJS doesn't ship with an officially supported toolbar, but there is ​a pseudo-official one that should do the trick.

It can't just be dropped in, though, because there are some conflicts between the version of SpreadJS used in that demo, and the current stable version that the WordCamp Spreadsheets plugin uses. It needs a bit of finessing to get the two to play nice together.

[iandunn]

This will be superseded by the upcoming Budgets plugin.