This reverts commit 3b5e03df.

Also added a version and extensions field to abi_def.

Removed action::current_action_data and PACKED macro since all actions are packed/unpacked according to the abi definition and cleanup of tests. GH #2350

initial draft of STL support for contract's code, doesn't work for now (STL is not in this repository)

fixes the issues with the deferred transactions and inline messages, implement changes to the proxy and a test case

* Fix simpledb contract

Under this approach the functions in simpledb.gen.hpp can be auto-generated using the ABI definition.

In particular the specialization for currentMessage must only be defined if the
struct has at least one variable length type (String, Bytes, etc), otherwise the default function will do ok.

The functions valueToBytes/bytesToValue must only be defined when the table is a KeyValue table.
These are required because the underlying db functions receives and
returns the serialized version of the value.

Then we can simplify the interface for the C++ helper VarTable (maybe reanaming to KeyValueTable?)
specifying the KeyType and the ValueType.

template<AccountName scope, AccountName code, TableName table,
typename KeyType, typename ValueType>
struct KeyValueTable

and inside the store/load functions (table_impl_obj) we need to call valueToBytes/bytesToValue accordingly.

Ref #492