The previous commit started the separation of the decoding process
into (a) reading the data from disk and (b) interpreting the data.
It also introduced part (a) as the process of creating the
RLPContractDetails object.

This commit completes the separation by doing part (b). As a result
only the interpretation of data remains inside the decode method of
AionContractDetailsImpl.

The unit tests for RLPContractDetails cover incorrect encoding size,
testEncodingIncorrectSize was no longer useful.

The VM type is required to interpret the contract details correctly.
It is now provided directly to the decode method instead of being
specified externally and requested via documentation.

DetailsDataStore has access to the physical databases where contract
data is stored. Since connecting the contract details object to the
data source must go though the DetailsDataStore it is best to perform
this operation when the instance is created.

Additionaly, this refactoring minimizes direct access to the databases
used by all contracts and reduces the mutability of the contract
details object.

The new AvmContractDetails is identical to AionContractDetailsImpl,
other than the class name. This choice was made to allow easily tracking
the evolution of the class towards supporting only AVM contracts.
Similarly, AionContractDetailsImpl will evolve to support only the FVM.

The DetailsDataStore is responsible for instantiating the correct version
based on the given VM type. To avoid incorrect cross-class casting, it
does not create a ContractDetails instance when the VM type does not
correspond to a supported VM.