mongo-jackson-mapper in an OSGi environment

[sandermak]

Two things:

1. There is a maven-bundle-plugin configured, but the resulting JAR after a mvn clean install has the auto-generated plexus-archiver manifest rather than the manifest generated by the maven-bundle-plugin.
2. For some use-cases, I need to manually convert my value object into a JSON object, see [1]. Since BsonObjectGenerator is currently not exported, I cannot do this. Therefore, the exported packages could be extended.

I created a pull request containing solutions for both these issues. It might be better to move the net.vz.mongodb.jackson.internal.object classes to a non-internal package and expose, rather than exposing the package directly as I did in my pull request.

[1] example:

JacksonDBCollection<JsonOutcomeResult, Object> outcomes = ...
BsonObjectGenerator bsonObjectGenerator = new BsonObjectGenerator();
try {
   new ObjectMapper().writeValue(bsonObjectGenerator, jsonResult);
} catch (IOException e) {
   throw new RuntimeException(e);
}
        outcomes.update(new BasicDBObject("testState.sessionKey", sessionKey), bsonObjectGenerator.getDBObject());