Updated decrementMinute to behave similar to incrementMinute such that decrement will first round down if current value is not a multiple of this.minuteStep.

**incrementMinute will apply the increment and then remove the remaining so that the new value is the next-step up (this.minute==2 with increment applied will result in "15" with a this.minuteStep==15).

Previous implementation would not round decrement (this.minute==2 and this.minuteStep==15 will result in the minute becoming "47" instead of "0".

Added UnitTest test-cases to test when the initial value is not a Multiple of the step for incrementMinute and decrementMinute

fixed formatting issues within the file