Refactor code duplication in load, loadBy and loadAny()

[romaninsh]

i need to refactor load(), loadBy() and loadAny() to merge them with tryLoad, tryLoadBy an tryLoadAny. But there are some considerations:

• tryLoad must throw and discard exception if the record is not found. It's CPU-expensive operation.
• exception from load() must include Query as it currently does
• tryLoad() failure should cause model to unload()
• load() should throw exception but not unload the model.

Given these conditions, I'm not sure who should call what. I'm thinking there should be an extra argument to Persistence->loadX that will indicate if the exception should be generated or if [] should be simply returned.