Calculator

- Simple calculator
- always ontop widget
- support expression + - x ÷ ( )
- support percent operation
- Memory buttons
- Scientific calculator
- Support digit grouping separator(comma, space, Apostrophe)
- Support digit grouping method (987,654,321.012 or 9,8765,4321.012 or 98,76,54,321.012)
- History list, restore last value

[Percent operation]
100x3%=3 (3% of 100)

[Memory buttons]
M+ : memory + result
M- : memory - result
MR : memory return
MC : memory clear
MS : memory set

[Clear button]
C : clear
AC : all clear (clear result and memory)

[Scientific Calculator]