chore: add model id

[sulheim]

Description of the issue:

I'm tired of getting the warning: '' is not a valid SBML 'SId'. every time I read in Sco-GEM. As dash ("-") is not valid SBML I suggest to add the id Sco_GEM

Expected feature/value/output:

No error message.

Reproducing these results:

If applicable, please attach any code used below (if it's matlab code replace the word "python" with "matlab".

cobra.io.read_sbml_model("Sco-GEM.xml")

To do:

If specific curations are proposed, generate a list of checkboxes of steps that should be followed to solve this issue:

• [x] Add id with model.id = "Sco_GEM"

I hereby confirm that:

• [x] This problem persists in the master branch of the repository
• [x] A similar issue does not already exist
• [x] I've considered asking this first in the Gitter chat room

[edkerk]

I suggest we append the version number: "Sco_GEM_v1.2.1", increaseVersion.py can then increase this with each release (see #118)

[edkerk]

Model version should only be included in the master branch, as intermediate models in the devel and child branches would not correspond to that version number anymore. So will add the model ID without versioning in devel and start including the version number when making release v1.3.0.

[sulheim]

Sounds good