Move all DI models to a new models/ directory.

The goal is that services/ should only include things that are part of
appContext that gr-diff might depend on.

Change-Id: I558b2b878bdb4cf853b779fbe641364c83565177
diff --git a/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.ts b/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.ts
index 18ef5a9..c8c9915 100644
--- a/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.ts
+++ b/polygerrit-ui/app/elements/shared/gr-comment/gr-comment.ts
@@ -56,7 +56,7 @@
 import {fire, fireEvent} from '../../../utils/event-util';
 import {assertIsDefined} from '../../../utils/common-util';
 import {Key, Modifier} from '../../../utils/dom-util';
-import {commentsModelToken} from '../../../services/comments/comments-model';
+import {commentsModelToken} from '../../../models/comments/comments-model';
 import {sharedStyles} from '../../../styles/shared-styles';
 import {subscribe} from '../../lit/subscription-controller';
 import {ShortcutController} from '../../lit/shortcut-controller';