add DBus.Properties interface introspection info

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[upower] call asynchronously GetAll() to retrieve properties

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
Merge pull request #23 from nemomobile/upower-async

[upower] call asynchronously GetAll() to retrieve properties