[kcms/users]: Don't hardcode the list of avatars

This replaces a hardcoded list of avatars with searching in $DATA_DIRS/plasma-avatars, which allows distros to ship their own avatars

BUG: 426777

kcms/users/CMakeLists.txt

@@ -3,4 +3,5 @@ add_definitions(-DTRANSLATION_DOMAIN=\"kcm_users\")
 add_subdirectory(src)
 
 install( FILES kcm_users.desktop  DESTINATION  ${SERVICES_INSTALL_DIR})
+install( DIRECTORY avatars/ DESTINATION ${DATA_INSTALL_DIR}/plasma-avatars )
 kpackage_install_package(package kcm_users kcms)