Upgrade to Polymer 1.9

Upgraded to the latest Polymer 1.9 version. Additionally changes from the latest polymer element yeoman template were applied and a bug in IE11 was fixed.

The 1.x.x versions of svg-piechart will support Polymer 1.x, while the 2.x.x versions will support only Polymer 2.x going forward.

The 1.x.x version will live in the 1.x branch, while the 2.x.x versions will live in the master branch