Add Maven Central backend

Adds support for having Maven projects specified by groupId:artifactId
Yes, I was wondering about the replacing of : . by /

Basically, I am a little wondering/afraid how likely are people creating for example, the project for:
``http://repo1.maven.org/maven2/plexus/plexus-compiler/`` to name it ``plexus-compiler`` instead of ``org.codehaus.plexus:plexus-maven-plugin``