GTM logic refactored

[maxsam4]

GTM logic has been simplified and made more flexible.
Some work will be required by the dApp team to incorporate the changes.

[coveralls]

Coverage increased (+0.04%) to 95.982% when pulling 94139b8 on gtm-logic-refactor into b205061 on dev-3.0.0.

[satyamakgec]

The approach is good on the contract side but it will little bit harden the dApp work. dApp team needs to create some scenarios (combination of true or false) when issuer wants to change in the transfers flag.
And redemption/ allowAllWhitelistTransfers will little bit costlier.

[maxsam4]

@satyamakgecallowAllWhitelistTransfers will actually be cheaper. Ones less SLOAD is required in the new logic.

Only allowAllTransfers and allowAllBurnTransfers will be slightly more expensive but I don't think anyone will use them in practice.