New plugin alignbtn

This plugin provides a new button ```align``` which

1. shows the current alignment of selected text and
2. allows changing alignment using a drop-down menu.

![screenshot from 2013-10-31 13 52 45](https://f.cloud.github.com/assets/229567/1445841/5b08621a-422b-11e3-84ea-afe16216088e.png)

Allows a more minimalistic editor appearance.