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
>  Any thoughts on how to migrate existing usage which uses to the wls prefix to a new prefix.

The [upgrader plugpoint](http://docs.xebialabs.com/releases/4.0/deployit/customizationmanual.html#repository-upgrades) is supposed to help with this kind of scenario. Another option I can imagine would be to release it with a different prefix, and then immediately create a branch in which the prefix is changed back to `wls` for compatibility with your customer setup.

The long-term overhead is obviously greater in the second case.