add set/get attribute
tabs to spaces, and added thrown exception
changed setattribute and getattribute to set and get
Tweak code to utilize get() and set() method.

Signed-off-by: crynobone <crynobone@gmail.com>
Merge branch '2.1' into 2.2

Signed-off-by: crynobone <crynobone@gmail.com>

Conflicts:
	src/Resources/Container.php