Store Tp nickname as nco:nickname on nco:PersonContact itself too
Store Tp nickname as nco:nickname on nco:PersonContact itself too

This allows to watch for changes only on nco:PersonContact and makes
everything easier as there's no need to keep relations between
nco:PersonContact and nco:IMAccount somewhere in memory.

Reviewed-by: David Edmundson

leonhandreke/ktp-common-internals,KDE/ktp-common-internals,KDE/ktp-common-internals,KDE/ktp-common-internals,leonhandreke/ktp-common-internals,leonhandreke/ktp-common-internals