Check if CI is added during register-ci

Sometimes due to the churn in staged-recipes, we get a feedstock that is registered twice. This means it could have multiple webhooks and/or multiple projects. This happens in particular with CircleCI and AppVeyor. In the case of CircleCI, it is just multiple webhooks. In the case of AppVeyor it is both with each webhook pointing to a new AppVeyor project. To fix this, we should check in advance to see if the project already exists and if we already have a webhook before proceeding further.