Disable public display of thread page in front end

Currently you are able to open ticket page through /?post_type=sf_thread&p=2
Corrected coding standards
Initialize $items by empty array

This is to prevent undefined variable error because $items which is
supposed to be an array is passed to other functions
Escaping data before echoing
Adding support for I18n
Add show thread option to specify if the tag should be shown in all
threads page

Conflicts:
	supportflow.php
Using wp_query to get count of threads

Current approach cause it to include thread replies in the count too
Using wp_update_post() instead of using $wpdb to update post modified time
Remove private option from filter links

They are just private replies to thread and are actual threads
Revert "Using wp_update_post() instead of using $wpdb to update post modified time"

This reverts commit 2cdc0e3a70c32d4cd92a0a3e0a47f0824ec40b83.
It was causing some bugs because it raise action_save_post() method
Updated plugin URL and authors in plugin file header
Preventing direct access to plugin by typing its URL

Currently anyone can execute plugin PHP code directly by typing
/wp-content/plugins/supportflow/*.php

Now it will die if anyone try to directly execute it
Remove wp_ajax_thread_attachment_upload action hook as callback function
was already removed earlier
Added a missing `>` to a HTML close tag
Corrected coding standards
Add actions to WP security nonce
Merge branch 'minor-changes' of https://github.com/VarunAgw/supportflow into 141

Conflicts:
	classes/class-supportflow-admin.php

Fixed merge conflict by manually removing `wp_ajax_thread_attachment_upload` callback, because it was removed in 4f89bf36c472f57f3b6420ee107704ef9971d7da.
Merge branch '141'

Fixes #141.