feat: [W12-151] upgrade for openzeppelin v2

[Hokid]

TODO:

• [x] Replace Ownable with Secondary
• [x] ReentrancyGuard moved to utils/
• [x] rename DetailedERC20 to ERC20Detailed
• [x] Use interfaces for ERC token, e.g. IERC20
• [x] Update roles systems
• [x] All state variables are now private to get value use getters
• [x] Some events renamed to past-tense (e.g. Burn -> TokensBurned)
• [x] Inherit methods from ERC20 in WToken, remove the same code that is in ERC20 contract
• [x] Check changes for test utils
• [x] New SafeMath.mod
• [x] increaseAllowance, decreaseAllowance in ERC20. Not important.