Shunting-yard algorithm

Ability to convert string equation into reverse polish notation
Fixed shunting-yard algorithm

Previous reverse polish notation conversion was incorrect
Solve Reverse Polish

Ability to solve equations with operators + - * / into double
Fix input always begins with 0
Precision of final result with BigDecimal

Final calculated result precision is fixed using BigDecimal.
However, does not erase trailing decimal zeros.
Bundle fixes

- Added debug textview
- Implemented error checking for open close brackets (User will never
input invalid brackets)
- Cleaned up error checking logic
Deleted debug messages & fixed bug #9

Fixed bug #9 Number won't display after an operator is displayed
Bug fix #7 - Error checking required at calculation
Bug fix # 11 Error message does not disappear
Bug fix #11 Additional changes

Moved debug message to bottom
Add more error checking for deleting error message after they appear