Generate a personal token on behalf of the user

[hmdfsn]

Description of issue or feature request
Users have to provide their personal tokens as part of the setup. To do so, they must generate a new token as follows (if not have already of if can't remember the existing one):

Github -> Settings -> Developer settings -> Personal access tokens -> Generate new tokens

Would be great if the extension does that on behalf of the user. This way the user herself does not have to take care of this procedure.
This issue might be addressed in accordance with #40.

Current behavior
The extension does not allow the user to generate the personal token on the fly.

Expected behavior
Allow the user generate the token during the installation rather than providing an existing one.
One possible solution is to obtain the username and password from the user, generate an access token on her behalf, store the access token and discard the password.

Related resources: [1], [2], [3].