feat: implement cross chain and oracle modules

[yutianwu]

Description

This pr implements two modules: crosschain and oracle:

• crosschain: Thecrosschain module manages the cross-chain packages created by other modules. It also maintains all the receive and send sequences of each channel. Othe modules can register their cross-chain apps to crosschain module, so that the cross-chain package from BSC can be dispatched to their apps and processed properly.

• oracle: Theoracle module processes OracleClaim messages from relayers. The OracleClaim messages are relayed from BSC which will be processed by the cross-chain app of the specific module. If the relayer is not in turn, the message will be rejected. The oracle module will also check the BLS signature of the signed relayers, if the proportion of signed relayers don't reach the threshold of 2/3, it will also be rejected.

Changes

• implement crosschain and oracle module