Refactor HTML syntax highlighter too keep track of tag nesting

This is needed for the eventual implementation of inline spellcheck
Start work on managing dictionaries in calibre
...
Add ISO 3166 country codes
...
Implement loading of both builtin and user installed dictionaries
...
Start work on dialog to manage user installed dictionaries
...
Start work on adding dictionaries
Add/remove for dictionaries from OpenOffice extensions  works
Implement renaming of dictionaries
Integrate the dictionary widget into the editor preferences
Keep track of the current book's locale as a separate global variable for performance
Refresh all editors after changing dictionaries