Code refactoring and removing general test and send mail buttons

Sendmailer, testmail, sendtest from user controller need to be moved to the newsletter controller.

Some of the actions from the newsletter controller and the actions mentioned above(from user controller) have repeated code, we can merge those actions and make them generalized.

Actions which can be generalized and merged are:
1. index, opt_in and opt_out
2. test_opt_in, test_opt_out and testmail(from user controller)
3. send_opt_out, send_opt_in and sendmailer(from user controller)
4. send_opt_in_test, send_opt_out_test, sendtest(from user controller)

Also the test and send mail buttons in the top_navbar are confusing, we can move them below individual newsletter beside the edit and delete buttons.