weblogic-certificate plugin

Initial version of the weblogic-certificate plugin

Introduces 2 new Containers:
- CustomTrustKeyStore
- CustomIdentityKeyStore

and 2 Deployables
- TrustCertificateSpec
- IdentityCertificateSpec

and an SSL Channel restart contributor
> Of course if we are to proceed on this, we would also have to indicate somehow that we don't support each mode.

We should hopefully be able to do that with good descriptions and in the README. I would guess the lack of the other properties would also make this clear, but I agree that it will raise questions.

> So how would you model having to choose one of the keystore modes and subsequently handling mandatory 
> properties per mode?

It's a tricky one. The best I can come up with is keeping the properties optional and adding a validator with good error messages to check that the selected combination works.

@ilx @bdevic @rklaren Your thoughts on this..?