Fix naming convention.
Initialize libmtp.
Expand the devicelist class.

The devicelist class now shows the list of connected MTP devices. There are
several pieces missing from the implementation, specially the pop-up signal
propogation to MtpcWindow.
Create the devicelist folder tree.
Fetch MTP devices and display in the folder tree.

This commit essentially adds the piece of code to display the list of
detected MTP devices.