Rename evaluators #454

Result of running following commands on previous commit:

    find . -name "*.*pp" -type f -print0 | xargs -0 sed -i 's/generic_json_evaluator_registry/custom_operation_interpreter/g'
    find . -name "*.*pp" -type f -print0 | xargs -0 sed -i 's/json_evaluator_registry/generic_custom_operation_interpreter/g'
    find . -name "*.*pp" -type f -print0 | xargs -0 sed -i 's/generic_evaluator/evaluator_base/g'
    find . -name "*.*pp" -type f -print0 | xargs -0 sed -i 's/set_custom_json_evaluator/set_custom_operation_interpreter/g'
    find . -name "*.*pp" -type f -print0 | xargs -0 sed -i 's/_custom_json_evaluators/_custom_operation_interpreters/g'
    find libraries/plugins -name "*.*pp" -type f -print0 | xargs -0 sed -i 's/_evaluator_registry/_custom_operation_interpreter/g'

    git mv libraries/chain/include/steemit/chain/generic_json_evaluator_registry.hpp libraries/chain/include/steemit/chain/custom_operation_interpreter.hpp
    git mv libraries/chain/include/steemit/chain/json_evaluator_registry.hpp libraries/chain/include/steemit/chain/generic_custom_operation_interpreter.hpp