Add service providers XML database support

It adds:

- a class to parse XML and retrieve elements.
- a class to retrieve long names from a system file.
- a class to control status when changing options and store selection using
	GConf.
Create tests for service providers classes
Add combo boxes to choose 3G service provider

It adds 3 combo boxes to navigate through service providers database XML
files using country, provider and plan.

It uses ServiceProviders model class to get previous selection, store new
one and populate surrogate options.