Add minimap feature

build/android/jni/Android.mk

client/shaders/minimap_shader/opengl_fragment.glsl

client/shaders/minimap_shader/opengl_vertex.glsl

src/CMakeLists.txt

src/client.cpp

src/client.h

src/client/tile.cpp

src/client/tile.h

src/defaultsettings.cpp

src/drawscene.cpp

src/drawscene.h

src/game.cpp

src/mapblock_mesh.cpp

src/mapblock_mesh.h

src/minimap.cpp

src/minimap.h

src/nodedef.cpp

src/nodedef.h

textures/base/pack/minimap_mask_round.png

textures/base/pack/minimap_mask_square.png