Server configuration overlays

Add a way for the server to parse multiple configuration files which are overlayed on top of each other in order:

./bin/server.sh -c infinispan.xml -c overlay.yml

• you can overlay as many files as you want
• you can use any file types you want in any order you want
• each file must be a full "infinispan configuration file" but it doesn't have to be a full server configuration as long as the end result is a proper server config
• there is no check for conflicts: each file is loaded on top of the other, overwriting any configs

for example, using the default infinispan.xml and the following yaml:

infinispan:   cacheContainer:     caches:       - distributed-cache:         name: "yaml"

you get the default server with a distributed cache called yaml