tst_serializer: Add structures.hpp as SOURCES for Tria to pick up
Nuria::Variant: Removed everything that's now doable using QVariant

Nuria::Variant now offers two methods, buildList() and stealPointer().
Features removed were:
 - Comparisons for types (See QMetaType::registerComparators)
 - Conversions for types (See QMetaType::registerConverter)
 - Iteration over lists and maps in QVariant (Works automatically)

Further, all uses of removed Nuria::Variant functionality was replaced
with the equivalents in QVariant/QMetaType.