Return the block level after broadcasting an operation

[DariusParvin]

The pytezos functions that broadcast operations in pytezos_contract_tester.py should return the level denoting the block height at which the operation was included in the blockchain. This functionality is missing and needs to be added.

[DariusParvin]

When this issue is fixed, it should be fixed in zeekoe as well. boltlabs-inc/zeekoe#203

[DariusParvin]

@kwf do you know if we can get away without needing the level?

if not, our other options are

1. Write something (using pytezos) that scans through blocks and returns the level of a recently confirmed operation.
   Pros - it wouldn't introduce any new dependencies.
   Cons - scanning through blocks is a slow process, and creating this function would require some digging into pytezos.

2. Using an open source API (from the same developers as pytezos)
   Pros - The API is straightforward to use and is faster than scanning blocks
   Cons - introduces a new dependency