Adds a new set of 'New Project' dialogs to allow authors to easily copy
keyboards from local filesystem, Keyman Cloud (including a keyboard
search web page, implemented in keymanapp/keyman.com#536), and
directly from a GitHub URL. Adds related documentation.
Fixes: #13073
Depends-on: keymanapp/keyman.com#536
1. Copy help.keyman.com/developer/17.0/* into /developer/docs/help
2. Update references to 18.0 where appropriate
3. Copy all referenced images from /cdn/dev into
/developer/docs/help/images and update links in documentation
Next commit: add deployment to help-keyman-com.sh. Note: simplest way to
test links at this point is to use the help.keyman.com auto deploy and
wait for the PR on help.keyman.com to be validated; we could look at an
internal link validation tool that verifies markdown links?
Relates-to: #12347
