Fixes before Beta

[mgratch]

• [x] add Multiselect UI on the view to allow the admin to determine which columns are sortable and whether they are ascending or descending.
• [x] Only show visible columns in Multiselect UI drop down
• [x] Ensure plugin only works with DataTable Views
• [ ] Make sure admin scripts are initialized when datatable view is selected for the first time.
• [x] Ensure admin scripts only fire on edit.php page while adding/editing a View
• [ ] Add failed background processing checks (health checks)
• [ ] Convert MySQL PDO code to MySQLi code ... i.e. the proper WordPress way
• [ ] Check for background processing library whether plugin or dependency
• [x] Remove index table when Views are trashed
• [x] Add uninstall function
• [ ] Add remove tables on uninstall setting
• [x] Enqueue creating index tables for existing DT Views on activation
• [ ] Make multi-select sort field UI sortable with drag and drop + touch
• [ ] General Code Clean Up
• [ ] Dynamically identify how many rows can be inserted at a time without causing strain on the server (currently it is processing 250 at a time and inserting 1 row)
• [ ] Add notice to GV edit.php table which tables are indexed

[zackkatz]

• [ ] Namespace tables; instead of queue and failed_jobs, perhaps gv_entry_index_queue gv_entry_index_failed_jobs
• [ ] Log activity using gravityview_log_error and gravityview_log_debug hooks, or something else like WP-Logging