Plugin base: Item list: Created provider handling methods.

In order to avoid the need to recreate these methods, and to support
archives provider handling methods have been moved to item list base
class. These methods provide easy way to create and retrieve providers
based on paths.
Plugins: File list: Adapted code to use new provider methods.
Plugins: Created archive support and moved ZIP provider.
Plugins: Archive support: Added missing init file.
Plugin base: Item list: Support for archive providers.

Create provider will now create archive provider if requests. Method for
releasing archive file handles was also created to allow proper clean up
on program termination.
Plugin base: Provider: Add archive handle and additional file mode.
Plugins: File list: Support for READ_APPEND mode in local provider.
Plugins: Archive support: Initial listing of ZIP files.
Plugins: File list: Report errors during directory loading.
Plugins: Archive support: Dirty initial existance check.