Disable pointer events on CodeMirror-lines.
Remove redundant ruleset.
Update comments.
Set text cursor.
Update CodeMirror SHA to brackets-sprint20 branch, which contains a temporary cherry-pick of a fix from upstream and avoids other fixes we don't want yet.
Merge pull request #2827 from adobe/glenn/close-dropdown

Fix dropdown closing
Update CodeMirror SHA
Update CodeMirror SHA. For real this time.