Adds ability to deploy geojson as maven dependency

* Updates build.gradle
* Adds maven and nexus gradle plugins
* Removes gradle-templates plugin (used for project setup only; website frequently down)

To deploy geojson jar to local .m2 repo run:

<pre>
$ gradle clean test install
</pre>

Then it can be included in your gradle project using:

<pre>
compile 'com.mapzen:geojson:0.1-SNAPSHOT'
</pre>

or maven using:

```
<dependency>
    <groupId>com.mapzen</groupId>
    <artifactId>geojson</artifactId>
    <version>0.1-SNAPSHOT</version>
</dependency>
```