Add break time between shifts

[shakram02]

If shifts follow this pattern => 'duration'+break
we can slide the start time of the next shift to the newly added shift, example:

** if break is 10 mins **

sh1 10:10AM -> 10:30 AM
then we generate shift2
sh2 10:40 -> 10: ...

** if break is 10 mins **
** if shift is 10 mins **
sh1 10:10AM -> 10:30 AM
then we generate shift2
sh2 10:40 -> 11:10 ** NOTE: wrap around time, this is not yet supported in the short-time-date class, we should create a function named addMinutes/subtractMinutes **