Vesting escrow wallet

[kostind]

Please check if the PR fulfills these requirements

• The commit message follows our Submission guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

What kind of change does this PR introduce?

Added VestingEscrowWallet module.

What is the current behavior?

(You can also link to an open issue here)

What is the new behavior?

(Define and describe any new functionality. Clarify if this is a feature change)

Does this PR introduce a breaking change?

No

Any Other information:

Shouldn't be merged before all tests will be fixed

[adamdossa]

@kostind - Couple of small questions - overall module looks great.

1. Please can we wrap transferFrom calls in a require statement. Not strictly needed as the ST will throw if there is a failure, but good practice in case the ST implementation were to change in the future (and more in keeping with the ERC20 spec.)
2. Any reason not to allow the sendToTreasury function to take an explicit amount in case you only want to transfer some unassigned tokens back to treasury (the function can check that the amount requested is less than unassignedTokens?
3. To avoid the loop in e.g. removeTemplate we could store the index of the template into templateNames in the Template struct. I always worry about unbounded loops ;-).

[kostind]

@adamdossa @satyamakgec All comments have been applied.

[satyamakgec]

@kostind everything is good once the test cases will successfully be passed. I will approve the PR

[coveralls]

Coverage increased (+0.07%) to 97.761% when pulling 0ecdf79 on Vesting-Escrow-Wallet into c85c599 on dev-2.1.0.