Fix friend class warning.
Reduce QML API, and use a global object for exposing current text checker
Style fixes
Dropped C++ API for changing current spellchecker

Now we directly access the Enchant spellchecker from our
implementation of WKTextCheckerClient. Also, simplified the API
for accessing textchecker properties. Now QWebGlobal only exposes
the variables textCheckerEnabled, textCheckerLanguages and
textCheckerAvailableLanguages, instead of direct access to the
Qt text checker.
Spellcheck changelog entries