Updated the osm-simplify tool to work on the coastline shapefile provided by the openstreetmap database.

Summary: The shapefile can be found at: http://openstreetmapdata.com/data/land-polygons

Test Plan: Still has some issues, like some polygons are rendered as linestrings inside Marble.

Reviewers: nienhueser, rahn

Subscribers: Marble

Tags: Marble

Differential Revision: https://phabricator.kde.org/D2007