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
> but this would still pollute the property space of the WebLogic Server container with a lot of properties from all
> the different keystore modes

If I'm understanding this code correctly, there are only three properties at present, which in a separate category doesn't seem to bad. But it's your call, of course: I was more interested to find out whether a `CustomKeyStore` represents something that a WebLogic user was likely to recognize, e.g. is it a configuration type in the WLS console it its own right?

If so, it certainly makes sense to model it here also. If not (i.e. if a WebLogic user was more likely to think of a keystore as something that was "part of" the server configuration), it might make more sense to leave it out.