Maven Indexer : support for configurable repos

Currently relies on Admin Config for OSGi.
I had to change some signature from `String[]` to `String` and rely on CSV convention for input, to be able to use OSGi properties support.
:japanese_goblin: Important lesson learnt: OSGi pid cannot contain `-` symbol. If you use them, itt won't throw any exception, it will just fail silently. So no longer `io.hawtio.maven-index-plugin`  !!!

To test quickly:
```
config:edit io.hawt.maven.indexer
config:proplist
config:propset repositories 'http://repo1.maven.org/maven2@central,http://repo1.maven.org/maven2@central2'
config:proplist
config:update
```


https://issues.jboss.org/browse/ENTESB-1487