Added some new functionalities and changed the design

- The equals button is now blue (inspired by Googles Scientific
Calculator)
- Added “.” (dot) functionality. Still WIP since only one dot should be
present at each operand.
- Added two new ON and OFF buttons for enabling and disabling the
calculator easier and with less code.
- Added DEL functionality. The calculator now deletes the latest
character on the text view.
- WIP with the arrow keys. It should place the cursor to the left or
right.
Quick update

Deleted the equals button colour in the equals button clicked function
since the code is more suitable (for our situation) in the MainWindow
base.
Updated design + other. Check description.

- Updated design - more intuitive. Color changed on button.
- Added PI functionality - Still WIP
Updated design
Annother design update
Added new functions.

- Added CheckSymbol - Making it impossible for multiple symbols in a row
Merge branch 'Update'

Conflicts:
	CoolCalc.userprefs
	CoolCalc2/MainWindow.cs
	CoolCalc2/gtk-gui/gui.stetic