Add check for purely backwards model to k_order_pert

The k_order_solver does not solve purely backwards models (as is the case in stochastic_solvers.m). But in contrast to stochastic_solvers, there is no check and no warning. Entering the mex-file then results in a crash of Matlab

Filter out cases where invalid starting value leads to NaN or Inf in Jac...

Replaces cryptic message "Some element of Newton direction isn't finite. Jacobian maybe singular or there is a problem with initial values" with more expressive message.

Added an option for setting the number of points where the posterior kernel is evaluated when using mode_check. Reorganized the options_ global structure wrt mode_check.

Reverted Ferhat's commit 23e583f95c0a5631c943c44f9116f20b91c0fb0a. The names of the dynSeries variables are stored in a column cell array.

Fixed bug in @dynSeries/align method (occuring if the second dynSeries object has more observations than the first one).

Reverted buggy commit 5366dd5cb9f546809ff21a0bd23a2ac423aac6ce by Ferhat and added call to strtrim in @dynSeries/extract method to remove leading and trailing white spaces in variable names.

Fixed bug. The cell of strings varlist had wrong dimension (must be a column) if the code is executed with matlab.