Document WebAppRegistry

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>
Port test case to new Diorite test framework

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>
Fix test /WebAppRegistryTest/test_install_packages

A warning about Empty 'categories' entry caused test failure.
metadata.json of google play package has been updated and others have
been removed.

Signed-off-by: Jiří Janoušek <janousek.jiri@gmail.com>