Tile management

Request for a Pull Request to integrate major functionalities in the master.

This implements:

1. Style Abstract Class along with a PolygonStyle implementation. 
The style constructs the vboMesh and adds these meshes to respective tile. These tiles owns a data structure which maps style to vboMesh.
2. tileManager functionalities of generating visible tile sets based on viewModule.
TileManager now populates the tiles to be read from the dataSource. It is also responsible to call the respective styles to fill meshes for individual tiles. 
3. Implementation of scenedirector owning the control of the application.
4. Implementation of GeometryHandler to get tesselated points, indices and normals.
5. Implementation of JsonExtractor to extract coordinates from Json features.