iframe.js: Update content in a more compatible way

[nilmerg]

The previous implementation was very error prone as it relied on the exact location of the existing content and updated content. If there was any difference, the update from the behavior didn't work correctly and produced an incorrect HTML hierarchy.

This will fix this so that the behavior is more compatible with how the content it is rendering is structured. I've also included basic support for Icinga DB Web, though this might be still subject to change. I hope to remember to notify you if this is the case. 🙄

The behavior should now work fine, as long as the following is the case:

• There's a .module-grafana iframe
• .module-grafana is a direct child of .content (or .content > .host-detail in case of Icinga DB Web)
• .content is a direct child of the content being rendered

[Linuxfabrik]

it works, thank you both very much :)