Python Add-in

I've created a simple Python Add-in for esri2open, which provides a menu and a simple set of buttons for the tools:

![esri2open-menu](https://f.cloud.github.com/assets/1314/715309/ef06be12-df16-11e2-8730-38965e8fb434.png)

This way, the package can be installed simply by double clicking on a generated esri2open.esriaddin file ([an example file](http://4326.us/esri/esri2open.esriaddin)), which can be created by running the `makeaddin.py` script.

This add-in will work at 10.1 and later. However, other than moving the .tbx and related files into the 'Install' subdirectory, this does not effect the running of the .tbx and associated tools in 10.0.

I've also added a logo for the project, based on the 'GeoJSON' twitter handle:
![esri2open-logo_32x32](https://f.cloud.github.com/assets/1314/715332/88be975a-df17-11e2-88c3-57a2d9bf55e3.png)