Proxy implementation

[ArtemKolodko]

1) Added new table contracts_proxy

create table if not exists contracts_proxy
(
    proxy_address               char(42)        not null,
    implementation_address      char(42)        not null,
    created_at                  timestamp not null default now(),
    updated_at                  timestamp not null default now(),
    unique (proxy_address, implementation_address)
);

2) Implemented new methods getProxyImplementation and assignProxyImplementation

• getProxyImplementation: checking for implementation for given contract address
• assignProxyImplementation: adding record to table contracts_proxy with implementation address assigned with proxy contract address