0-index versus 1-index

[spratt]

CodeMirror stores lines in 0-index format, whereas the backend stores lines in 1-index, which leads to lots of off-by-one errors.

[Gankra]

I would wait on this until way have absolutely settled on continuing to use CodeMirror.

[cdelahousse]

We may be changing syntax highlighter. This issue depends on that change. This issue will remain open until we've resolved that issue.