Make sure QGIS can reload the underlying lib

[gacarrillor]

Add __init__.py to libs/ so that QGIS understands we've got a subpackage in libs/ and can reload it when reloading or upgrading the plugin.

Fix #33

[gacarrillor]

Steps to reproduce the solution to the problem:
(see steps to reproduce the problem)

1. Download pg_service_parser.0.1.7_mod.zip (this version writes whitespaces between the = sign in the pg_service.conf file), BUT, it has a libs/__init__.py file to let QGIS know we've got a package it has to unload when unloading the plugin.
2. Install the ZIP from 1) and make sure it is activated (i.e., that you see the plugin icon in the plugins toolbar).
3. Use the plugin to write on the pg_service.conf file.
4. Verify the spaces between the = sign. This is expected.
5. Go to Plugin Manager -> All, search for pg service. Select the plugin from the list and click on Upgrade plugin.
6. Repeat step 3).
7. THIS TIME you won't get spaces between the = sign, which is the behavior we expect since 0.1.9 (the one the plugin was upgraded to) already has a fix for that.