Chainlink funding rate oracle

[134dd3v]

• Abstracts the funding rate override logic out of VPoolWrapper through FundingRateOverride library, exposing only set and get methods.
• Adds ability to supply an address as funding rate override. This is to prevent breaking storage changes.
• Adds absolute bound of 100% (annual) to the funding rate, it's added in the getFundingRateAndVirtualPrice method. This implies that funding rate will stay within ±100% (annualised), even if real and virtual prices are very apart, oracle gives weird values or funding rate override value is set ridiculously high.