[#171] Unify aeson instances generation and drop aeson-options

Description

Problem: In many cases we use aeson's defaultOptions, in one place we use defaultOptions from aeson-options.

1. It seems better to use consistent options unless there is a good reason to use something different somewhere (currently there are no such reasons).
2. aeson's defaultOptions is not quite good for us because usually our record fields have prefixes derived from their names which are quite redundant in JSON.

Solution:

1. Define morleyAesonOptions based on aeson-casing. It drops prefix from record fields. Use it everywhere.
2. Remove aeson-options since it's not used anymore.
3. Update manually defined JSON encoding of ContractState to drop prefixes.

Related issue(s)

Resolves #171 (closed)

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