CRM-13964, CRM-13965, CRM-13973

This PR consists of implementation of issue http://issues.civicrm.org/jira/browse/CRM-13964.

Also this PR consists of 75% implementation of http://issues.civicrm.org/jira/browse/CRM-13965 issue.

PR also consists of work of CRM-13973.

Major part of the implementation includes financial BAO method modification and few addition and using specific paramters passing to them which are responsible for triggering the partial payment code execution and making additional payments.

note this is without test cases, will be submitting a PR soon for it.