(PE-5502) Support for loading chained certificates into a KeyStore

This commit adds support for loading a chain of certificates into the
same entry in a KeyStore.  This includes the following changes:

* An overload of the associatePrivateKey() method on the
  CertificateAuthority Java class was introduced to enable passing in
  multiple certificates to be stored in the KeyStore entry.

* All of the certificates found in a Reader passed into a call
  to associatePrivateKeyFromReader() will be used in the certificate
  chain stored in the KeyStore entry.  Previously, if more than 1
  certificate was found in the Reader, an `IllegalArgumentException` was
  thrown.
This is starting to drive me crazy @camlow325 - remember it's not a hard-and-fast rule, and it doesn't make much sense when the lines above and below it are longer anyway.

Not going to block the PR for this, but still :D