bump hash to sha512, add comment
add levels of detail tutorial, bump lod thresh to 3000
reduce lod thresh to 1500, my laptop could be a little sluggish
Merge pull request #640 from twosigma/spot/security-review

bump hash to sha512, add comment
Merge pull request #641 from twosigma/spot/633

document level-of-detail feature
Handle moving markdown editor up and down

fixes #350

Due to the way that epic editor works and the way that moving elements
via the cellmanger you need to reinit the markdown editor to reshow the
markdown content.