net-im/libquotient: flavorize port for Qt 5 and Qt 6

• To allow for co-instability, the header files have been moved to a prefix. This location might change again in the future, if upstream adapts their build system for co-instability.

• The android related file is simply not cared about in the Qt6 version, to allow for co-instability.

Approved by: adridg