- start using `GET` and query parameters instead of `POST` when
meaningful
- inline parsed protocol data and metadata in block headers
- inline parsed protocol data and metadata in operations
- split the RPC in four categories:
- static data, available explicitly in block headers and operations
- static "metadata", information that were computed while validating
a block or an operation, but which are not explicit in the block
header (e.g. the baker of a block, the list of internal
transfer... (currently not implemented, but that's WIP))
- "context" all the static data we may read in the context
(contracts balance, list of delegates, ...)
- "helpers" are some RPC that may perform some computation.
Added a block_service and corresponding handler in the node to perform
queries of the form '/blocks/<id>/raw_context/<path>?depth=<n>'
returning the sub-tree corresponding to <path> inside the context of
block <id>. The parameter <depth> controls the size of the tree,
default is 1.
