Add xdg-open (and friends) abstraction
Implement set of abstractions to handle opening uris via xdg-open and similar helpers used on different desktop environments.
Abstractions are intended to be included into child profile, together with bundle abstractions such as ubuntu-browsers, ubuntu-email and others, for fine-grained control on what confined application can actually open via xdg-open and similar helpers.
Edited by Vincas Dargis