Fixed the 1=0 error

Typing a number without an operator and pressing equals would  always
give zero. I fixed that by equating the answer variable to the number
variable before even considering any operators in the equals method.
Fixed small visual glitch error

Calculation 1+2=3+ would update the display to read 2+ after the second
plus instead of 3+. Needed to equate variable displayNumber to answer
variable.