Add settings interface for CodeMirror plugins

[leoj3n]

• http://codemirror.net/doc/manual.html#addon_active-line
• http://codemirror.net/doc/manual.html#addon_selection-pointer
• http://codemirror.net/doc/manual.html#addon_continuecomment
• At 80 or 120 chars:
  • http://codemirror.net/doc/manual.html#addon_rulers
  • http://codemirror.net/doc/manual.html#addon_hardwrap
• http://codemirror.net/doc/manual.html#addon_tern
• http://codemirror.net/doc/manual.html#vimapi