Fix one index with multiple topic urls

[gonwan]

Use attachment for testing.

Some chm files have one index name links to multiple topics. Just align behavior with hh.exe.

Urls with CJK characters work fine.
In addition, index are now sorted, and the index tree widget scrolls to the matching item to top when searching.

testindex.zip

[gonwan]

With second commit, internal files are ensured to use internal encoding. The attachment is a chm file with gbk internal encoding and utf-8 text encoding. Select Chinese Simplified (UTF-8/GBK) to view.
The index tab is also refreshed when changing encoding.

testencoding.zip

[u-235]

I think the src/dialog_topicselector.ui file was accidentally included in the PR; the only significant change in it is the line <?xml version="1.0" encoding="UTF-8"?>. And one more thing: it would be nice to add an empty line before the ParsedEntry::clear function.

[gonwan]

I think the src/dialog_topicselector.ui file was accidentally included in the PR; the only significant change in it is the line <?xml version="1.0" encoding="UTF-8"?>.

Other *.ui files have this line. A newly created one also has this line. I also deleted some redundant space, and make the dialog wider, since some index titles are so long. I think the file was modified incorrectly by some misconfigured tools.