Add cache path variable from Java

Use cache path for db location
Add Assetbridge to extract asset files to cache path
Fix SSL by using extracted ca bundle
Use file:// style URL using extracted styles

android/cpp/NativeMapView.hpp

@@ -14,6 +14,8 @@
 namespace mbgl {
 namespace android {
 
+extern std::string cache_path;
+
 extern jmethodID on_map_changed_id;
 
 extern jclass lon_lat_class;