Consistently return 'count' as a string

The underlying Problem DBus service returns 'count' value as a string,
therefore the Problem proxy must use a string for missing value.

Related to #83

Signed-off-by: Jakub Filak <jfilak@redhat.com>
Give the designed look to the sidebar

Multi-selection remains unimplemented until gtk-3.14 is out.

Fixes #83

Signed-off-by: Jakub Filak <jfilak@redhat.com>