Add OSGI plugin to generate bundle metadata

[badfish69]

A trivial change to build.gradle to enable the OSGI plugin.
This allows the generation of OSGI bundle metadata in the resulting jar file, which in turn resolves classloader issues when running bouncy-gpg in OSGI environments.

[neuhalje]

Hi @badfish69 , thank you for the contribution. According to the plugins website it is deprecated:

This plugin is deprecated and will be removed in the next major Gradle release. New builds should not use this plugin.

1. Maybe the bnd plugin is an alternative?
2. Do we need any more configuration?

[badfish69]

Ah - that's annoying.
This is the first time I've tried to do this with gradle. I normally work with maven.

The bnd plugin appears to be the answer, which requires slightly more configuration but is still pretty simple. I'll close this pull request and submit a new one.

[neuhalje]

I‘ll give it a shot this weekend. If it works I can do a release. Is there anything else to do/needed for osgi integration? Could you maybe add a README.osgi.md file with some examples and instructions? Nothing fancy.

…

On 13. Dec 2018, at 08:04, badfish69 ***@***.***> wrote: Ah - that's annoying. This is the first time I've tried to do this with gradle. I normally work with maven. The bnd plugin appears to be the answer, which requires slightly more configuration but is still pretty simple. I'll close this pull request and submit a new one. — You are receiving this because you were assigned. Reply to this email directly, view it on GitHub, or mute the thread.

[neuhalje]

(Added as PR #29 )