TACHYON-120 Fail to cast String to other objects for JsonObject

Currently JsonObject.get just directly cast parameter Object to the generic T type. 
This could generate class cast exception such as the one from String to DependencyType.

Modify the code to use Jackson JSON formatter instead by passing the Class<T> type in the get method to avoid Java type erasure to get the actual parameterized type.

Extra fix:
Fix Javadoc parameter name
Remove unneeded Javadoc exception throwing
Unfortunately, no you can't because of Java erasure [1]. 
The Jackson's TypeReference allow to maintain the generic type [2] like List<String> or List<Integer>.

[1] http://docs.oracle.com/javase/tutorial/java/generics/genTypes.html
[2] http://www.programcreek.com/java-api-examples/index.php?api=org.codehaus.jackson.type.TypeReference