Also add support for "gutter" in add/removeLineClass.

Issue #2920

Issue #2915

Issue #2919

The mode associated with a token is now the inner mode at
the time when the token is started. The htmlmixed and markdown/gfm
modes were fixed to return empty tokens during mode switches
when necessary to enforce this rule.

Issue #2919

Defaults to `window`

Issue #2922

Issue #2921

Issue #2888

This also helps closebrackets close quotes

Closes #2918

See http://discuss.codemirror.net/t/html-hints-not-working-just-after/45/6

Issue #2912

You won't get much effect from setting the mode option when
no modes are loaded.

Issue #2909

Issue #2914

without this pressing / and then Esc doesn't clear status line

Issue #2908

Issue #2903

Issue #2904

The color white is not visible on the current backgroung

Workaround for an error in getting to insert mode.  It was very difficult to reproduce, and I don't know
what led to it, but the ">" mark was set but returned undefined when find() was called.  This should work
around the problem if it happens again.

Issue #2901