refactor ScipyEigenvalueSolver, ScipySGEigenvalueSolver
refactor ScipyEigenvalueSolver, ScipySGEigenvalueSolver

- ScipyEigenvalueSolver uses dense or sparse scipy linalg functions, new method
  option, support extra options
- ScipySGEigenvalueSolver uses dense lapack functions, remove force_n_eigs
  option
- imports moved to .__init__() for early failure

rc/sfepy,BubuLK/sfepy,sfepy/sfepy,lokik/sfepy,sfepy/sfepy,lokik/sfepy,lokik/sfepy,RexFuzzle/sfepy,lokik/sfepy,RexFuzzle/sfepy,vlukes/sfepy,sfepy/sfepy,RexFuzzle/sfepy,BubuLK/sfepy,BubuLK/sfepy,rc/sfepy,RexFuzzle/sfepy,vlukes/sfepy,rc/sfepy,vlukes/sfepy