[WebUI] Fix base path not being honored

[DjLegolas]

Twisted requires a child as bytes, not str to work as expected. In addition, it adds the ability to call base in an infinite loop of calls, i.e. hostname/base/base/base/....

The solution is to build the tree as served.

This is an alternative PR to #390.

[DjLegolas]

Just noticed that serving both root and base is by design for both local and reverse proxy usage... So this PR is relevant if we want to keep the behavior... (🤦 on myself...)

[DjLegolas]

Ok, so now there will be no more infinite loops

[cas--]

Can you elaborate on what this is fixing?

[DjLegolas]

Sure. Currently, if you set a base path (--base tmp) for the WebUI, you will get the following URL http://1270.0.1:8112/tmp. Now, if you will add another base (http://127.0.0.1/tmp/tmp), the page will be loaded as usual, even though there is nothing in that URL. This can be used to enter unlimited amount of children to the URL.

[cas--]

Ah I see! So I wasn't happy about adding a hack to a hack so crafted a simpler solution with tests: 4b6ac1f4c4

Let me know if I have missed anything with the implementation