adding core PZP information API

jira issue: wp-227
Change use of object as key

Use the sessionId as a key instead.

Jira Issue: wp-737
Avoid corruption of unicode strings

The message is accumulated in string parts, which might break if the buffer boundary happens to be in the middle of a multi-byte char. Instead, accumulate the data in a buffer and convert it to a string when it has all been received.

Jira issue: wp-737
Fix bug in callbackStorage

Jira issue: wp-748
Merge pull request #456 from TobyEalden/wp-737

Fix PZH message handling
Merge pull request #458 from TobyEalden/callback-fix

Fix bug in callbackStorage
Merge pull request #454 from krishnabangalore/wp-227_corePZPinformation

adding core PZP information API