Methods for all "get" api calls

Added the following methods:

	getDevice 		- shortcut for $netsight->{soap}->getDeviceByIpAddressEx('ip')->result()->{data};
	getAllDevices	- Returns hash table with IP address keys pointing to WsDevice table.
	exportDevices	- Returns hash table with IP address keys pointing to a hash table parsed from a NGF from the exportDevicesAsNgf API call.

See perldoc Enterasys::NetSight for more details.