Feature/purchase reminders

[robertjensen]

This PR adds a purchase reminder facility to cinfdata as suggested by Asger Barkholt Moss

To install, create an extra dataplot table named dateplots_purchase_reminders:

CREATE TABLE `dateplots_purchase_reminders` (                                                          
  `id` int(10) unsigned NOT NULL AUTO_INCREMENT,                                                       
  `time` timestamp NOT NULL DEFAULT current_timestamp(),                                               
  `type` int unsigned NOT NULL,                                                                
  `value` double DEFAULT NULL,                                                                         
  PRIMARY KEY (`id`),                                                                                  
) ENGINE=MyISAM AUTO_INCREMENT=1 DEFAULT CHARSET=latin1;                                               
grant all on nanomadedata.dateplots_purchase_reminders to 'mail_alarm'@'%';

Remember to change nanomadedata to the name of your database.

Install the python3 QR package:
sudo apt install python3-qrcode

Cinfdata will now recognize email alarms with a description starting with [purchase_reminders] as a purchase reminder and show them in the overview on the order.php page. From here you can generate QR codes that when activated will increase a counter by 1 and thus trig the email alarm.

Sensible defaults for an email alarm is something like this;
Description: [purchase_reminders]Order chocolate turtles
Check: q0 > p0
No repeat interval: 86400
Parameter: 0.1
query: select unix_timestamp(time), value from dateplots_purchase_reminders where type=25 order by id desc limit 1

Email body something like this:

It has been reported, that we are out of chocolate turtles!!

Once you have ordered new ones, reset this alarm by pressing this link:
http://cinfdataurl/cinfdata/other/order.php?id=25&action=reset

Notice that for now, there is no mechanism to insert the expected type-id into the select statement and the email. This will normally be the existing highest id + 1. This is confirmed when the alarm is created and can easily be changed if it was something else.