✨ add spellcheck toggle

[kevinansfield]

closes TryGhost/Ghost#8461

• adds toggle spellcheck button to the gh-markdown-editor toolbar
• adds custom styles to fake a spellcheck icon
• updates simplemde fork
  • adds spellcheck to the list of toolbar buttons that don't have their active class removed based on cursor position
  • removes bundled marked dependency that we no longer use

TODO:

• ensure button doesn't lose active state when cursor is placed in content

[coveralls]

Coverage decreased (-0.09%) to 71.299% when pulling 9b68d77 on kevinansfield:spellcheck-toggle into fac2560 on TryGhost:master.

[coveralls]

Coverage decreased (-0.09%) to 71.299% when pulling a7debf6 on kevinansfield:spellcheck-toggle into 24c02ac on TryGhost:master.

[aileen]

It seems like the initial state (first load and after refresh) of the spellcheck box is active, but doesn't work.

[kevinansfield]

@AileenCGN that's the way CodeMirror's spell check works - it doesn't trigger the spell check until first edit and the behaviour is the same with or without this PR. If we want to fix that it's probably worth opening a separate issue.

[aileen]

Ah... Ok. I just found it very confusing, because it seems to be activated, but isn't until I toggle the spellcheck off and on again.

[kevinansfield]

There's an open issue on the spell checker plugin here sparksuite/codemirror-spell-checker#28 - proposed solutions (one of which is almost a complete rewrite) haven't been incorporated into the main library. We could fork the spell checker plugin and incorporate a fix into our own simplemde fork if needed.