Fix: AccountsController#modifyAccount

* The account associated with the principal submitting the request
must be same as the account being modified else return a 401
to the client

* Updated tests to reflect change in signature in AccountsController#modifyAccount
and AccountsService#modifyAccount

* Do not use the DTO mapping when modifying an Account as this causes
NestedException to be thrown and subsequent transaction rollback. I suspect
this is because of the deep hierarchy & cyclic references in the Account model
Change type last_login column to TIMESTAMP

* Set the last login date upon successful login

* Remove unnecessary namespaces in web-context.xml