Add support for 0.6 features

[montyly]

https://solidity.readthedocs.io/en/v0.6.3/060-breaking-changes.html#solidity-v0-6-0-breaking-changes

Among others:

• Functions override (virtual , override)
• abstract contract
• receive / fallback function
• payable type conversion
• try/catch statement

[elenadimitrova]

Just got a false positive for the following try/catch statement we added:

        uint256 decimals;
        try IERC20Extended(_token).decimals() returns (uint _decimals) {
            decimals = _decimals;
        } 
        catch (bytes memory /*lowLevelData*/) {
        }

Error:

TokenPriceProvider.getEtherValue(uint256,address) (modules/common/TokenPriceProvider.sol#33-46)
ignores return value by IERC20Extended(_token).decimals()
(modules/common/TokenPriceProvider.sol#36-41)

[montyly]

Hi @elenadimitrova . Thanks for reporting this. I am tracking it in #511, and will fix it as soon as possible.