Support signing chained transactions

[ilblackdragon]

With evolution of various standards that include Storage management, callbacks, etc - we are ending up needing to issue multiple transactions in a row to different contracts.

Even though NEAR's transaction supports multiple actions per transaction, all of those actions apply to the same receiver.

Simple example is sending nDAI via linkdrop v2.

Next transactions must be sent:

• call send on linkdrop to initiate storage
• call ft_transfer_call on nDAI to transfer to linkdrop

More complicated example: add liquidity of nETH, nDAI and nUSDT to Multiswap.

Next transactions must be sent:

• to multiswap to register this user's account for storage
• to nETH to send funds to multiswap
• to nDAI to send funds to multiswap
• to nUSDT to send funds to multiswap
• to multiswap to actually add liquidity to the specific pool

User should confirm signing once in the wallet the whole set of transactions to different contracts and Wallet would play them out.

If Wallet sends them all at once, even though they have increasing nonce and will be played in the right order, because they contain async calls - next tx may start executing before previous tx's async calls finished.
For now submitting them one after another is required but ideally we would have better protocol solution for this.

[vgrichina]

note that this is technically is already supposed to be supported

however we didn't test it much end to end, UX might be suboptimal, etc