Port SavingsManager contracts from `master` to `master-v2`

[alsco77]

Is your feature request related to a problem? Please describe.
Recently this repo was ported from solc 0.5.16 to 0.8.x, and truffle/web3.js to hardhat/ethers.js.

There are a number of contracts that have not yet been migrated, and will be used in future product releases.

Describe the solution you'd like
This issue proposes that the SavingsManager.sol is ported from master to master-v2. This includes:

• porting of the solidity file and all dependencies
• refactoring to bring code in line with solc 0.8 (e.g. removal of SafeMath)
• porting of relevant test cases to new repo (TestSavingsManager.spec.ts)

[doncesarts]

I think this is already done by #167 ? Is not it ? @alsco77

[alsco77]

Ah yes, good catch @doncesarts , some of these issues are ood