Tinymce update with upstream

[es]

This PR updates our fork of TinyMCE to the latest upstream master. I made a clean fork of upstream and cherry-picked our commits over. I left out commits that fixed bugs already fixed in upstream. Commits cherry-picked over:

• Fixes HTML mangling while stripping data-mce helpers (f423a2a)
• Updated readme (87865ae)
• Added noparsing plugin (41eff28)
• Fixed compile error in noparsing plugin (cb4abc5)
• prevent serialization in setContent (669d841)
• prevent removal of empty elements in DOM parser (e40de13)
• Prevent bogus br from being added to empty RTE content (e540911)
• Set node to current context if undefined (9234e6f)
• Add optional CSP header to Editor iframe (f51b9c2)

There are some tests that test for things we want/don't want in Admin. I commented them out, but would be happy to just delete them too:

• 'Remove redundant br elements'
• 'Invalid inline element with space before'
• 'Parse no attributes span before strong'

Since this branch rewrites the history of master It'll have to be a force push.

@angelini @nsimmons

[nsimmons]

Let's merge this once we've tested it out in Shopify and let it run in production for awhile. Just in case this update becomes problematic.

[es]

Added CircleCI config so now we're encouraged to modify & track changes with tests.

[EiNSTeiN-]

I'm a bit late to the party but my commit f51b9c2 was merged upstream already, it didn't need to be cherry-picked, this will cause the 'load' event to be fired twice.

[EiNSTeiN-]

the double 'load' is because the upstream patch was implemented slightly differently due to upstream code changes.

[es]

So can I simply extract your commit or are there changes that need to be done?

[EiNSTeiN-]

Yes, removing f51b9c2 should be good enough, changes are already in def4d31

[es]

@nsimmons @angelini ?

[angelini]

🏇 💨

[nsimmons]

Everything running pretty smooth so far.