Reenable slither on wallet contracts and updates to make nightly build pass

[elenadimitrova]

Reenable slither on the ./contracts/wallet contracts which was disabled due to crytic/slither#405

Ignored two warnings raised by slither on the already deployed ArgentWalletDetector contract:

INFO:Detectors:
0: getImplementations() should be declared external:
	- ArgentWalletDetector.getImplementations() (infrastructure/ArgentWalletDetector.sol#112-114)
1: getCodes() should be declared external:
	- ArgentWalletDetector.getCodes() (infrastructure/ArgentWalletDetector.sol#119-121)
Reference: https://github.com/crytic/slither/wiki/Detector-Documentation#public-function-that-could-be-declared-external

And one on the VersionManager

0: init(address) should be declared external:
	- VersionManager.init(address) (modules/VersionManager.sol#221)
	- UpgraderToVersionManager.init(address) (modules/UpgraderToVersionManager.sol#59-76)
Reference: https://github.com/crytic/slither/wiki/Detector-Documentation#public-function-that-could-be-declared-external

Green build: https://app.circleci.com/pipelines/github/argentlabs/argent-contracts/1446/workflows/55e8a7dc-1ec9-49f0-a885-1ab6fc3dcb8a/jobs/1765