abstract MBPage class added

This class includes common functionality that all the pages should have.
For instance navigation functionality that can be done from all the pages.
eg: logout, go to configure tab
Integration test for https://wso2.org/jira/browse/MB-850

This test case test whether admin with a different admin role name is recognised as an admin
role in the server.

Test Steps:
     * Admin role name is changed to "Administrator" using user-mgt.xml and restart server
     * Log in to admin account and create a queue, "testQueue"
     * New user, John, created with admin privileges.
     * Log out from admin account and log back in with john account
     * Browse the "testQueue". Since john is an admin he should be able to view the queue.
Merge pull request #81 from Asitha/mb-850

Integration test for https://wso2.org/jira/browse/MB-850