Fix various errors

[KeesCBakker]

This PR fixes some problems:

• Fixes the way we construct the full URL, especially when people end the host with a /. The new expandUrl helps to create a URL that is acceptable.
• Error handling: in some cases Grafana will return an HTML page, we don't want that as part of our error object.
• When the first API call of getUidBySlug errors out, this can cause an infinite loop. We now break on the first problem. Also, paging was broken, so if you have +5000 dashboards, you could not get the right dashboard.

[stephenyeargin]

so if you have +5000 dashboards, you could not get the right dashboard.

... That's a lot. 😅 I sure hope they are programmatically created, and that the template feature in Grafana was explored.

[stephenyeargin]

May fix #105