prevent non-english chars are encoded. Fixes #50

- firstly, the `idfilter()` is applied at `ns` and `hns` which are already cleaned by `cleanID()`
- secondly, `idfilter()` is applied at `id` and `hns` of items that are page ids as existing at file system.
For all these cases no encoding is required. 

In dTree.prototype.addNode in indexmenu.js these id's are compared with the page id from $JSINFO
https://github.com/samuelet/indexmenu/blob/master/scripts/indexmenu.js#L205

I think it is not useful to keep the encoding (and solve this issue with decoding in dTree.prototype.add)

@samuelet can you review this and merge if it is fine?