[IMPROVED] Better handling of archived shares

Please check the appropriate ticket #1021 for details of the changes
made. Tested locally with shares created via INSERT.

Fixes #1021 after merge.
[IMPROVED] Debug logging for purgeArchive calls
[UPDATE] Mention Markdown on Newspost creation
Undefined property: Notification::$mail

I'm not 100% sure this is a bug, but I'm getting the following error from my crons.

> PHP Notice:  Undefined property: Notification::$mail in /var/www/MPOS/public/include/classes/notification.class.php on line 158

> PHP Fatal error:  Call to a member function getError() on a non-object in /var/www/MPOS/public/include/classes/notification.class.php on line 158

It appears the `Notification` class extends the `Mail` class instead of `Base`, in which case `$this->mail` does not exist.
Merge pull request #1050 from headzoo/patch-1

Undefined property: Notification::$mail
Added one more Option to  "Ajax Data Interval", for better performance management
[FIX] fixed 3 Notices
Merge pull request #1051 from Fredyy90/patch-5

Added one more Option to  "Ajax Data Interval", for better performance management
Merge pull request #1053 from Fredyy90/patch-6

[FIX] fixed 3 Notices
[FiX] Division by zero warning on $dNetworkHashrate

When not connected to a wallet, the value of $dnetworkHashrate is set to 0, which causes a division by zero error.
Merge pull request #1057 from headzoo/div_by_zero

[FiX] Division by zero warning on $dNetworkHashrate
Merge pull request #1029 from TheSerapher/issue-1021

Issue 1021
[FIX] Fix cleanup with 0 matching shares
Update README.md

Updated features and some minor content update.