Add encoding info (statusbar pane) to file compare

This patch adds new statusbar panes for encoding for file compare.

Currently there is no way to see a file encoding in file compare. Which is a major drawback sometimes. As WinMerge transparently handles unicode and ANSI files user might not have any clue which kind of files one is editing. Especially this is important to know when editing files with different encodings. Say unicode and ansi files.

Folder compare has selectable columns to show encoding so if file compare was opened from folder compare user might know encodings. But if files were directly opened to file compare (from explorer, from 3rd party software) it is impossible to determine the encoding.

So I consider this as a important usability improvement.