Fix distinction between initial values provided to dyn_ramsey_static.m and stale unchanged initial values in oo_.steady_state

In case of no steady state file, they are identical, but with a steady state file, they are not. Moreover, this fixes a problem with the dimension of the input to the steady state file. ys was not initialized and had wrong dimensions
Also adds comments to file.
Add unit test file Ramsey with auxiliary variables

TBD: add check for correctness. As variables are dummy variables, the solution should be identical to the one without these auxiliary variables
Update unit test by adding also auxiliary variables on exogenous variables
Merge pull request #770 from JohannesPfeifer/Ramsey_aux_vars

Ramsey aux vars