Added simplify circuit functionality and tests

[imagoulas]

Description

Added new functionality to simplify quantum circuits in place. The implemented simplifications include:

• removal of adjacent involutory gates
• combining rotational gates
• replacing adjacent square root quantum gates with their square
  The simplification algorithm also accounts for symmetrical control two-qubit gates.

To facilitate the process, a new function has been added that takes as input two Gate instances and returns a tuple of types bool and int. The boolean denotes whether the two gates commute and the int the possible simplification scheme.

User Notes

• [x ] Features added
• Changes to compilation (if any)

Checklist

• [x ] Added/updated tests of new features
• Removed comments in input files
• [x ] Documented source code
• Checked for redundant headers/imports
• Checked for consistency in the formatting of the output file
• [x ] Ready to go!