Modular cache configs

[andrus]

Most things in Bootique are modular, meaning multiple modules can participate in assembly of the final "service". JCache should not be any different. We should allow multiple modules to define their own cache configurations, that should all be presented as a single merged config to the end user.

I can see two possible directions for solving this issue:

1. Bootique may provide an uber CacheManager that internally routes between a map of CacheManagers by cache name.

2. Bootique may learn how to merge provider-specific configuration resources into a single config file that is passed to the single cache manager. E.g. EhCache XML structure should allow us to combine multiple <cache> elements together.