Merge pull request #11 from reydelleon/bulk_actions

Implements delete and send email bulk actions. The second one is still untested.
Merge pull request #13 from reydelleon/bulk_actions

Refactored some code to comply with standards and and reduce complexity.
Refactored to after renaming constant RLM_RSVPlus_Admin::FORM_ACTION_NEW_ATTENDEE to RLM_RSVPlus_Admin::FORM_ACTION_NAME_NEW_ATTENDEE.
Moved logic to process bulk actions from class-rlm-rsvplusattendee-list-table.php to class-rsvplus-admin.php. Changed manage-list.php view according to this changes. Overrided methods in attendee-list-table to support the logic move. Changed form method from get to post in bulk actions form. Fixed problems with actions lingering do to get parameteres not changing in the URL. This closes #10 and lays the ground work to solve #9. Most of the logic is in place, but needs some more work.