Adding and using a local version of the Montserrat web font

... so that we can present our slides offline, with the proper font.

I tested offline with chromium and firefox.

I noted a glitch when using firefox with a file:// protocol (directly reading from the filesystem, not from a server like one started with "python -m SimpleHTTPServer"): depending on the reload, the font is not found/applied.
I actually use exactly the same approach with my (deck.js) presentations and have not seen this problem before so I don't know from where the glitch can come from.

If some people can test it and confirm they see the glitch or not, we could decide based on the reproducibility of the problem. Anyway, it is still better than using the online font only.

Cheers,
Rémi