Add call to check if app is installed to remove banner

[sudoFerraz]

Currently the application is not able to verify if the user has already installed the GithubApp on his profile or organization.

Therefore, the banner on the overview dashboard does not disappear after the user has changed its settings.

This issue should create logic that verifies such installation, and removes the component from the overview dashboard if the user has successfully installed the app to allow private repositories.