Add is_algebraic assumption

See http://en.wikipedia.org/wiki/Algebraic_number
Adopt test: (sqrt(3) + S.Pi).is_rational is False
Add is_number property for AlgebraicNumber
remove using of new assumptions in the polys module
Deduce algebraic fact with Gelfond-Schneider theorem

See http://en.wikipedia.org/wiki/Gelfond%E2%80%93Schneider_theorem
Deduce algebraic facts with Lindemann-Weierstrass theorem

See http://en.wikipedia.org/wiki/Lindemann%E2%80%93Weierstrass_theorem
Fix Mul._eval_is_irrational: zero case
Add is_transcendental assumption

fixes #8000
Add Q.transcendental
Merge pull request #8049 from skirpichev/is_algebraic

Add is_algebraic assumption