Render line-ending invisibles on empty lines

Fixes #2857

Including correct interleaving with indent guides.
Merge pull request #2867 from atom/ns-react-empty-line-invisibles

Render empty line invisibles in React editor
Remove stray logging
Use default implementation of ::destroy from theorist Model class

Move actions that need to happen on destruction to ::destroyed hook.
Emit editor:will-be-removed event when unmounting the React editor
Only autoscroll in model when adding selection in React editors

Fixes atom/find-and-replace#245
Fix autoscroll specs for addSelectionForBufferRange
Upgrade to language-coffee-script@0.25
Default cursor on scrollbars.

Fixes #2876