Migrate to async aptos_sdk

[ikapeykin]

following the discussion from PR:
#10 (comment)

So, looks like we really need to implement these methods as async. I assume during migration process we can implement classes like:
AsyncAptosSdk, AsyncBridge, etc

to allow backward copability for others who already use this code

@unordered-set looking for ur feedback as well :P

[ikapeykin]

Confirming,

0.7.0

• [Breaking Change]: Removed the hex function from AccountAddress. Instead of addr.hex() use str(addr).
• [Breaking Change]: The string representation of AccountAddress now conforms to AIP-40.
• [Breaking Change]: AccountAddress.from_hex and PrivateKey.from_hex have been renamed to from_str.
• [Breaking Change]: Delete sync client
• Port remaining sync examples to async (hello-blockchain, multisig, your-coin)
• Updated token client to use events to acquire minted tokens
• Update many dependencies and set Python 3.8.1 as the minimum requirement
• Add support for an experimental chunked uploader

Needs workaround

[unordered-set]

Well, to address this properly I think we should
A) branch current master to sync-aptos branch and hardcode the version 0.6 in requirements
B) switch to async / 0.7 in master