Remove plottable-dev.d.ts from bower.json

The presence of two definitions files was causing trouble for
Typescript consumers downstream.

Developers interested in extending the library should probably pull
plottable-dev.d.ts directly from the repo.
Release version 0.28.1
Merge pull request #1006 from palantir/release-0.28.1

Release 0.28.1 (--> master)