implement hashCode method for HWISessionItem

HWISessionItem overwrites equals method but not hashCode method.
It violates java contract below:
"If two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result."
Currently equals and compareTo methods use sessionName in their implementation.
sessionName.hashcode() can be used in HWISessionItem.hashCode as well.