page-er

Following changes are made: The code of the element and demo examples are changed to work with Polymer 1.7. The demo examples using the element is changed to use the element (it might be an heir of the element). The structure of the element is changed to match the structure of other polymer elements (for instance, seed-element). The demo example is removed since it does add any value. Customization of pagination controls is reached by using the Polymer.Templatizer behavior. But most likely it has to be changed later even though it works. It feels like pagination controls should be defined as a separate element which can be substituted if a user wants to use a custom one. Tabs are replaced with spaces. , , properties became computed properties. Anyway, they have to be calculated from other properties. The demo examples using the element to demonstrate the routing integration were significantly refactored and simplified. It seems the used to fire a event right away, now it fires this event when the hash gets changed. It will be good to write tests, but this PR is already huge, therefore, I think tests can be added in a separate PR. :blush: I am looking forward to hearing the feedback.