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
Use a different prefix and package name? This makes it look as though this may be part of the standard WLS plugin, which could be confusing.

@vpartington Thoughts on that..?