Fix "remember password" feature

[aveao]

Right now, while saving the password to the keyring works perfectly (when "Remember Password" is picked), loading from the keyring fails.

There's 2 issues at hand here:

• gi.Secret.Service doesn't work async on python for some reason. The _final never fires. I could replicate this issue on a variety of distributions. So to fix this, I moved those functions to the relevant sync methods. While this isn't ideal, it fixes the bug at hand. gi.Secret.PasswordStore does seem to work.
• The .secret and .attribute functions of Secret.Item objects give out gi.overrides.Gio._DBusProxyMethodCall objects, not the actual contents. I ended up using .get_secret().get() (returns bytes) and .get_attributes()["user"] (returns str). I feel like the change on user especially was important, as the last one involved a for loop through the entire array.

This PR fixes both of them. Tested and confirmed working.

[zdohnal]

Hi, looks good to me, thank you for contribution!