Fix mbcs encodings

[gonwan]

Fixed multiple encoding related issues, changes:

• Now selecting encoding in menu only changes text encoding, not internal encoding(the one to work with #TOPICS). Use options like UTF-8/GBK to change internal encoding. This should be less confusing, since internal encoding is auto detected and not supposed to change in most cases.
• Fix garbage in webview titles. Now extracted directly from html, not #STRINGS.
• Fix possible garbage strings when viewing source and searching html content.
• Index entries with multiple Name are supported.
• Index entries shares one Name are supported. They are merged into one tree item, and a selection dialog is shown on click(same behavior as hh.exe) .
• Index are sorted, in alphabet.
• Scroll to matching item to top when searching index.
• Naming fixes, etc.

[u-235]

The changes to lib/libebook look interesting, but they'd be better split into multiple commits and put into a separate PR.

Now I am working with code from src/webengine and src/webkit and there are a lot of changes, so no other changes to this code will be accepted for now.