Resolves #1139: can use a direct permalink to a specific level

[pomeh]

This resolves the issue #1139 I just created, about permalink to levels.

I did not add unit tests as I didn't find anywhere query arguments are tested. But I've manually tested my changes through Gitpod (which is simply amazing !).

I also was thinking about a "share level" feature, but:

• this another feature
• this is out of scope of the initial issue
• this can have many implementations possible, and different UI design too
• this idea would need your validation first, before any change

Feel free to let me know what you think about all this.

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[pcottle]

Looks great! I also think this will work if you provide both a command and a level param, which is nice :) and the level one will run first too!