Cleanup maven dependencies and some configurations.

[splatch]

Extract version placeholders.
Introduced dependency management.
Improved OSGi packaging (via maven placeholders).
Removed dependency to netty from OSGi bundle.
Cleaned up license/developers section as it was duplicated.

[tolbertam]

Hi @splatch, it looks like we have some compatible goals! Quite recently I created #297 that was merged in yesterday to extract versions into properties defined in the parent module so they may be overridden. Per project guidelines would you mind rebasing against 2.0 and reopening the PR request against the 2.0 branch?

[olim7t]

Regarding your changes to the OSGI configuration, we want to keep shadedArtifactAttached=true: upcoming features like JAVA-640 will leak Netty to the public API, so they will require a non-shaded JAR; we still want to provide the shaded JAR for users not interested in them.

[splatch]

I wasn't aware of JAVA-640, I will update pull request to keep shaded JAR.

Also will rebase to 2.0 branch.

[splatch]

I updated commit for 2.1. For 2.0 branch is not yet done cause I started from never branch. Backporting is harder than merging.