Decouple the search implementation from the waves persistence logic.

The goal of this patch is to decouple the search implementation (SearchProvider) from the waves accessing logic (WaveMap). It should allow for alternative implementations of search providers - not dependent on concrete implementation of waves loading and access. The biggest problem with current implementation is that it requires to load all waves into memory on the server start up. An alternative (not memory based) search implementation would allow to load the waves lazily and evict later.