Keyring - username and password remember issues

Right now we have the 'Remember username and password' widget disabled since we couldn't fix the existing issues.

Running from the bundle, the keyring only recognizes the encrypted-file and plain-text keyrings. It makes sense, since from the library path it can't access to the @gi@ module required for using the gnome-keyring, also can't access to @PyKDE4@ which is required to use kwallet (kde's keymanager), and so on... For more information you can take a look at keyring's code at: https://bitbucket.org/kang/python-keyring-lib/src/

I tried linking the system's @gi@ library inside the virtualenv and I got access to the gnome-keyring. Adding gi to the @postmkvenv.sh@ (https://github.com/leapcode/bitmask_client/blob/develop/pkg/postmkvenv.sh) LIBS array did the trick.

I'm thinking that this problem may appear just in the bundle, installing bitmask from a .deb may work just fine (need more tests). If that's the case, we can disable the 'remember' for the bundles and later on work in a fix.

Also, we need to get rid of some code in the @keyring_helpers.py@ since we choose 'SecretStorage' keyring without checking if it exists or if it is usable. We should rely only in the keyring choosen by 'keyring' and exclude the OBSOLETE/not-use-this ones.

(from redmine: created on 2014-07-25, closed on 2014-07-31, relates #4083 (closed), relates #3898 (closed), relates #4190 (closed), relates #4864 (closed), relates #5985 (closed), relates #6879 (closed))