Plane class
Removed trailing spaces
Merge https://github.com/sympy/sympy into plane
Changed the are_perpendicular and is_parallel method
Refactor code in projection_line method
XFAIL the test in test_args
Removed the XFAIL
Added Dummies and used free_symbols() instead of is_constant()
changed Dummy() to Dummy
Removed Trailing Space error
Merge pull request #7667 from akshayah3/plane

Plane class