Returning wp_mail result after sending E-Mail
Return invalid E-Mail ID's in extract_email_ids() method too

Earlier it accept an array of E-Mail ID's and return only valid E-Mail
ID's from them. Now onwards it can also return invalid E-Mail ID's as
argument
Allow forwarding a thread to an E-Mail ID

It covers:
* A meta box in view thread page which allowes entering E-Mail ID to send E-Mails
* Sending thread replies along with its details to these E-Mail ID's
* Checking if user has permission and CSRF check
* Validating E-Mail ID's before sending
Add explainatory messages for user to failed ajax requests
Added action to wp_create_nonce()
Merge pull request #137 from VarunAgw/forward-conversation

Add the ability to forward a conversation.

Fixes #18.
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.
Bump version to 0.2.
Checking if post exists before accessing its properities

Currently if you view an non-existing thread e.g.
/wp-admin/post.php?post=25456&action=edit `$the_post` returns null causing
an error

So this commits check if it is null before continuing