Give users an option to create GitHub/GitLab token during the installation

[hmdfsn]

Description of issue or feature request
The user should provide the personal token during the installation which may add some complexity for the user. It would be a good idea if the extension gets the token transparently (without involving the user).
This issue can be fixed in accordance with #28.

Current behavior
During the setup, le-git-imate asks the user to provide the personal token and gives no option to generate it on the fly.

Expected behavior
Allow users to generate the token during the installation.