Changes: added functionality, design, code cleanup

After conflicting github copies - working again.

Added functionality:
- Made it possible to do multiple calculations using the line/string in
the textview1 instead of doing multiple single calculations in a row. -
Deleted “addition” function since no longer needed. - IMPORTANT!
- Made a factorial function and changed it to work with the new label
system.

Design:
- Changed the main background to white
- Added a label above the textview that holds the calculation string in
order to have an intuitive and sexy calculator.

Code cleanup:
- Deleted some unneeded and unused code.
- Added comments in the code for easier code reading