Trying to fix Travis CI configuration
Added LinRes.to_tf() to return a selected transfer function
Updated IPython notebook
Moved routines specific to Dymosim and OpenModelica to new file
Multiple changes:

- get_values, get_times, get_arrays now accept i=None to return all samples
- added get_values_wi_times and get_arrays_wi_times
- removed get_indices_wi_times