simpler solutions for a class of quartic equations

    Added ``roots_quartic_euler`` giving simpler solutions of the quartic equation
    
    For a class of quartic equations the Descartes-Euler method gives simpler solution.
    For instance

```
>>> from sympy import S, Symbol, Poly, count_ops
>>> from sympy.polys.polyroots import roots_quartic
>>> x = Symbol('x')
>>> sol = roots_quartic(Poly((x**2 + x + 1)*(x**2 + 4*x + 5), x)); sol
[-1/2 - sqrt(3)*I/2, -2 - I, -2 + I, -1/2 + sqrt(3)*I/2]
>>> count_ops(sol)
16
```

while currently in master ``count_ops(sol)`` is ``275``.