Add makeshift code to incorporate loaded solution into cobra

Fluxes read from the external solver's output file are read in
with this code. However, I haven't included dual solutions and
the plain flux list (sol.x) is unlikely to be useful. The sol.x_dict
will be, though.
Replace status_dict with status_list

Status should be provided by the external parser in the expected
format. This program should just check for these forms rather than
using a mapping to achieve it (since the mapping can't be the same
for different external solvers).
Create function to write LP problem to a file

Writing the LP is best done right before solving it since it
can still be modified after creation and before solution. Placing
the code in a function improves readability even though it will
be called in only one function.
Write problem immediately before solving with external solver

This is the correct time to write the problem since the model may
be updated after running "create problem".
Add exception handling in reading solution file

When the solution is not optimal, there cannot be expected to be
any lines in the solution file beyond the status line. After reading
the status line, the code now has exception handling for the case
where the rest of the file may be empty.
Load duals from external solver output

The output file should have a blank line after the primal values
before listing the dual values in the same tab-delimited format.
There is still no checking to make sure values have been entered
for all the variables.