converters.h: Make the default toJson() less greedy
converters.h: Make the default toJson() less greedy

template<T> toJson(T&&) grabbed even things that it cannot convert, leading to unpleasant effects in a situation when all that was needed was one implicit conversion (e.g. from QList<QString> to QStringList). So now it's three trivial toJson() overloads instead of a template.

QMatrixClient/libqmatrixclient,QMatrixClient/libqmatrixclient,Fxrh/libqmatrixclient