Retirement protocol - primary retires

Signed-off-by: Vidhoon Viswanathan <vidhoon@cs.utexas.edu>
Basic Client session  manager impl
(Not tested)

Signed-off-by: Vidhoon Viswanathan <vidhoon@cs.utexas.edu>
Session guarantee

Read your writes

Uses local session manager which records tentative & stable writes and uses them
to serves client during a session providing "read your writes" guarantee
even while switching servers.

Signed-off-by: Vidhoon Viswanathan <vidhoon@cs.utexas.edu>