Exponent bits max and min

[mmoult]

Currently, the exponent cannot have fewer than 1 bit. That is necessary. Right now, the down button is still pressable if the exponent is at 1, but it just won't do anything. We should make it more responsive and disable the down button if exponent is 1.

We should have a max exponent size, but I don't think we do. In fromDecimal, we use ints to calculate the exponent bits. Int max is 2,147,483,647, which is 2^31. That means that we shouldn't have more than 30 exponent bits allowable (which should also disable the up exponent button in addition to preventing a higher number).

[mmoult]

To my knowledge, we don't need to have a fixed max for mantissa bits, but we should disable the down button when it reaches 1 (just as mentioned for the exponent bit).