Hamster plugin doesn't remember its configuration

[Olivier Mehani]

The Hamster Time Tracker Integration plugin does not remember configuration settings.

Steps to reproduce:
1. Launch GTG
2. Edit/Plugins
3. Enable Hamster Time Tracker Integration, and keep it selected
4. Click Configure plugin
5. Change any of the preferences in the new dialog (I tend to choose GTG tag, Default to GTG tag if activity is unsorted, GTG task title, and leave GTG tags already used in Hamster).
6. Click Close
7. With the Hamster Time Tracker Integration still selected, click Configure plugin again

Result: All preferences are reset to their default.

Expected result: Preferences should have remained to the just-selected values.

More details:
* ArchLinux x86_64
* Python 3.4.0 (default) or 2.7.6;
* GTG dev commits 30950a3 or c9f89a9;
** build from AUR: https://aur.archlinux.org/packages/gtg-git/ (updates to the latest Git commit when building);
* Hamster TT 1.04 from ArchLinux repos.