Enabling Standalone Jar File For Distribution

I refactored the code layout to support distribution of the MapBox Android SDK via a single JAR file.  The JAR file is built using Gradle's 'android-library' plugin so a .AAR file is also available should people want it / as it and the Android toolsets become more mature and supported.  To build just run

```
gradle clean assembleRelease
```
From there just extract classes.jar from the MapBox-Android-SDK.aar in build/libs and rename it to mapbox-android-sdk-version-x.jar .

This all was done by 

* Consolidating the MapBox, OSMDroid, and Maki code bases into one standard Maven / Gradle project Java structure.
* Refactoring MapBox Marker loading of Maki objects via Java IO Streams instead of Android's getResourceById() as the latter isn't possible in non Android projects.  Mirrors OSMDroid's approach.
* Separated SLF4J dependency from codebase so that it's managed by user's project to help avoid transitive dependencies.

Updated the mapbox-android-sdk.jar file and QuickStart with more information.