Fix failure to display URLs ending in question mark

[Jaifroid]

Fixes #654.

I discovered that Kiwix JS does not exhibit the problem described, and it turns out to be that using encodeURI(), unlike encodeURIComponent() does not encode question marks. The problem here is the need to encode a question mark when it is part of the dirEntry's url or title, as will always be the case in Wikipedia ZIMs. But in fact, because even Zimit does not have a concept of a querystring, even if a querystring is present in the URL, that we always need to encode the full dirEntry.url before placing it in the iframe's location.href field (or redirecting to it in separate tabs). So, we have to use encodeURIComponent() but taking care not to encode forward slashes! This is how Kiwix JS does it, by encoding the parts between forward slashes.

Hopefully this will work in all circumstances and ZIM types, but it does need careful testing.

[Jaifroid]

I've tested in OpenZIM, Zimit1 and Zimit2 contexts, and all seems to be working.