Set default validator OFA share to 50%

[jj1980a]

This sets the default refund share to 50% instead of 0.

Public method getValidatorRefundShare should be used by frontends to retrieve a validator refund share (instead of former public accessor validatorsRefundShareMap).

[BenSparksCode]

Not sure if int instead of uint for validatorsRefundShareMap is an intentional choice or not. It looks safe as it is now, just unexpected var type

[jj1980a]

Not sure if int instead of uint for validatorsRefundShareMap is an intentional choice or not. It looks safe as it is now, just unexpected var type

The intent is to set the refund share to 50% by default for all validators.

As validatorsRefundShareMap map is holding 0 values for all entries, we add DEFAULT_VALIDATOR_REFUND_SHARE to each of them (when calling getValidatorRefundShare).
When a validator calls updateValidatorRefundShare to set a new value, we subtract DEFAULT_VALIDATOR_REFUND_SHARE from that value and store it in validatorsRefundShareMap.

E.g. a validator calls:

updateValidatorRefundShare(1000); // Sets share to 10%

The validatorsRefundShareMap entry for this validator will be 1000 - 5000 = -4000.
And when calling:

getValidatorRefundShare(aboveValidator);

It returns -4000 + 5000 = 1000.

Hence validatorsRefundShareMap can hold negative values yes.
We could define DEFAULT_VALIDATOR_REFUND_SHARE as an uint or an int, either way, it will have to be casted in updateValidatorRefundShare or getValidatorRefundShare.
It does feel funny to have it as an int when all other constants are unsigned, I'm not against switching it to an uint.

[BenSparksCode]

Hence validatorsRefundShareMap can hold negative values yes.

Cool, this looks good to me then. I can't see any security issues caused by this. We can leave it as is imo.