Update iOS precompiled libtess2 to include architectures for iOS devices
Merge branch 'master' of https://github.com/tangram-map/tangram-es
Loading of Hierarchy tiles

Added functionality to generate hierarchy tile ids for a visible tile based on the quad tree details mentioned
"http://wiki.openstreetmap.org/wiki/QuadTiles".

TileManager::UpdateTileSet is responsible to load the visible tiles, and once every visible tile is loaded, it calls
generateBufferTiles to load hiearchy tiles corresponding to itself.

There is implicit priority for visible tiles based on how threads are created and retreived data is processed.

Also if a new tile becomes visible, it is first checked in the buffered set of tiles before asking the service for the
data

Since tileData could be shared between m_bufferedTileSet and m_tileSet, its now a shared_ptr instead of a unique_ptr.

A bunch of other misc changes were done to make use of more c++11 feature sets.

TODO: We need to clean the buffered set of tiles and also implement disk caching.
Skip already loaded buffer tiles

Updated TileManager::generateBufferTiles to ignore loading buffer tiles if these were already loaded by another visible
tile(s) in the set.
Merge branch 'contzoom' of https://github.com/tangram-map/tangram-es into contzoom

Conflicts:
	core/src/tile/tileManager.cpp