Fix template ambiguities in aron_conversions

Fixes template ambiguities in libraries/aron/core/aron_conversions.h:

Before, e.g.

template <class T>
void toAron(T& dto, const T& bo)

and

template <class DtoT, class BoT>
void toAron(std::optional<DtoT>& dto, const std::optional<BoT>& bo)

were both applicable to toAron(std::optional<T>, std::optional<T>) which led to compile errors.

Needed for Implement 'PointAt'-skill (sw/armarx/skills/control!53 - merged)