A generic table class

It generate a simple table with minimal options
Using class SupportFlow_Table to create tables
Prevent race condition of cron jobs

It locks a temp file while cron is executing cron. In case cron completes
or process get terminated unexpectedly lock is opened allowing other crons
to proceed

Fixes #74
Add option to filter unassigned (with no owner) tickets
Merge pull request #149 from VarunAgw/cron

Prevent race conditions during cron jobs
Allow only limited HTML tags in `no_items` message of tables
Using wp_query to query database

Instead of querying database manually using $wpdb
Using get_posts() instead of using $wpdb
Removed unused code
Merge pull request #154 from VarunAgw/minor-changes

Add option to filter unassigned tickets
Merge pull request #148 from VarunAgw/tables

Reuse a generic WP_List_Table rather than duplicating individual ones.
Create dashboard widgets for SupportFlow

It covers:
* PHP Class to add dashboard widgets
* Two widgets
* - Widget to show recent tickets
* - Widget to show ticket assigned to current user