Updated syntax tree & project setup

Refactored syntax tree
- Created nodes for unary/binary operators
- Replaced iterator node from loop statements with a tag
- Removed indexed_expression under expression as it is
  already contained in variable_expression

Added new screanrio setups for running different files with or
without the --tree option

Added a return statement visitor to set the return value of a
subwaffle

Improved IDEA view
- Added structure view
- Changed to Dark theme
  (Revert from: File.Settings.Apperarance&Behaviour.Appearance)

Moved the old statements from simpleprogram.waf
to statement_test.waf