Make datasources for Grafana dashboard configurable

[Ornias1993]

Does what is states on the tin.
Adds a little selectionbox up-top to select the datasource instead of hardcoding one.

[mgdigital]

Thanks, looks good and I'll test it when I get a chance. Just a couple of small things:

• could you revert the casing change to bitmagnet?
• should the next version be 2 rather than 3?
• what is that "id": 79 referring to?

[DyonR]

• Shouldn't names be cased like names?

It just a style choice to have bitmagnet all lowercase. For example, the brand adidas is also stylized with all lowercase.
You would also write BitTorrent and not Bittorrent, and you also wouldn't write QBittorrent, but qBittorrent. It are all style choices of the authors.
Edit:
One more example (to give a Dutch example); bol, formerly known as bol.com, is also a brand which uses only lowercase letters. (except in the history section and if sentences start with bol)
You can see bol only written in lowercase: https://pers.bol.com/nl/het-verhaal/