fixes #407

fixes double-text on highlights in PDFs

smooths last difference between the jquery and pure dom xpath

fixes #409
closes #410

- Use the reify decorator to cache results of expensive Store calls
  made during displayer rendering.
- Re-work the displayer to have annotations more like the threading
  on the client. In other words, pass the whole annotation, not just
  the fields in the the displayer.

- Change `drag.canDrag` to `drag.enabled`
- Track when dragging ends to reset the delta measure point
- Remove dragstart event which won't fire in the host

- consistent use of font family variables
- consistent use of variable-ized $white color
- make use of the heading variables
- make .nav-tabs subsume tabbox mixin
- drop underlines from links (let's try it)
- unify .content and media queries
- extract noise class

Fixes #387

proof of concept only. for localwiki.

Needed a stop marker after the threshold, so that the area above
the top bucket (under the toolbar) doesn't show as having annotations.