Implement proxy for `dom/*` using the new `sig/setup` and `sig/teardown` introduced in troopjs/troopjs-core#142.

Refactor `sig/initialize` and `sig/start` to use `when.map`.
Rename `$HANDLER` to `PROXY`.

Remove `CONSTANTS`.

Make it IE friendly via `.charAt`

Use `STAR` constant.

Named some methods, did some renames.
Added modified timestamp for dom handlers.
Revised JSDoc.
JSDoc updates
Refactor `on`/`off`
Added tests for dom event handlers on widget.
Adapted to use the new decorator for on/off interception.
Reorder deps.
reuse `set_modified`
Merge pull request #56 from troopjs/feature/$on-and-$off

Refactored $on and $off to utilize event handler setup/teardown.