`setPrices` doesn't enforce precision

[exp7l]

Impact: High

Expected and actual behaviors of the system:

As per comment of setPrices, setPrices should uncompact the signed uint32s and scale by 10 ^ 30. and a precision.

// From the comments of setPrices:
// '''Oracle prices are signed as a value together with a precision, this allows
// prices to be compacted as uint32 values.
// The signed prices represent the price of one unit of the token using a value
// with 30 decimals of precision.'''

But, the code doesn't do these because the code doesn't enforce precision and trust the inputs. The trusted oracles can inadvertently or maliciously provide price updates that are of the wrong precision if there is no external price feed for comparision.

A concrete example of the exploit:

Because of bugs in oracle software, every trusted oracles provide ETHUSD updates at 4 decimal precision instead of 18. Assuming there is no external price reference to compare, the Oracle.sol accepts the min and max medians. Positions depending of the price feed will deem ETHUSD price has crashed, and the position will be liquidatable.

CVL property violated:

getPrimaryPriceComplyPrecision

[teryanarmen]

It doesn't trust the input blindly, it trusts that there's a configured precision for each dataProvider. This is by the current design.