Create Dataclasses for Spec Blocks

[bgunnar5]

The specification file is loaded in using dictionaries for each block and a json schema file to validate them. If we're going to open the Python API then it would be better to load in each block using a data class and a post_init method for validation (if necessary). Each block's data class could even have sub classes (e.g., StudyConfig -> StepConfig, MerlinResourcesConfig -> WorkerConfig, etc.). This would likely be good to work on at the Maestro level first and then propagate up to Merlin.