Added support for different file encodings

The title says it all.

- Added iconv-lite
- New ini setting editor.encoding
- Failback to utf-8
- UI Header shows active encoding
Remove this line and implement encoding autodetection. The libraries I've found are `https://github.com/mooz/node-icu-charset-detector`, `https://github.com/btd/node-detect-encoding`, and `https://github.com/runk/node-chardet` (which I prefer because it is written in JS and does not require any external libraries).