Use master function lyapunov_solver.m to call individual solvers

Johannes Pfeiferrequested to merge
JohannesPfeifer:lyapunov into master

Closes #821 (closed) by switching to Schur-based method by default when iteration fails. Closes #1077 (closed) by moving call to Matlab's dlyapchol and to disclyap_fast to master function lyapunov_solver

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