Add initial implementation of unattached annotations

A bunch of things (including CSS styling) is still missing.
Comments: fixed bug on deletion caused by improperly attached fake highlight

This sorted out the priblem mentioned in the comments of #115.
Remove debug output. Refresh comments.
Forbid empty comments.
When commenting, preserve the state of the adder icon
Bugfix: Comment icon was shown for replies too.

The ng-hide expression was extended for the comment-icon with checking whether the annotation has references.
Bugfix: Do not attach replies in the (bottom) comments heatmap tab.

- Added 'references' for the whitelist for transferring this to the host frame.
- We're only applying the FakeCommentRange and HighlightRange for annotations which are not replies.
Do not show orphaned annotations in the comments tab.
Do not show comment related alerts for replies during annotation save.
updateHeatmap(): Separate bucket for comments at the bottom of the page.

The heatmap.updateHeatmap() was altered to create a separate bucket (similar to above and below) for comments. This bucket cannot be merged with the other buckets.
Standalone page enhancement for comments

Standalone page now hides the quote field when it is empty and the annotation.text field is shown and 100% width
Enchance stream compact view for comments.

The streams (user, tag) do not display the quote when it is empty.
Enhance stream detail mode for comments.

Now the detail mode of the streams hides the quote when it's empty, and grows the text field, to 100%.
Removing unecessary extra character added temporary for anchoring comments.
UI design for comment bucket in heatmap

- Added a separate svg file (called comment_tab.svg) for the comment bucket.
- Reduced the space between the lower and the comment buckets
- If no comment bucket is shown, then the lower bucket is shown nearer to the bottom of the page.
Invoke draft protection when starting to comment
Merge pull request #660 from hypothesis/115-unattached-3

PR for Unattached annotations (=comments) V1