Add reminders

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Problem

Users may reply to not all bot messages.

Solution

Periodically remind a person with @username to reply to each message.

Command

Add the /set_reminder_period command to set periodic reminders for replying to bot messages.

Example: /set_reminder_period 2:30 - the reminders period will be 2 hours 30 minutes.

Scenarios

Without reminder

1. A user replies to all three messages
2. The bot sends a message @username, I wish you a productive day!

With reminder

1. A user with @username doesn't reply within the reminder period.

2. The bot sends a reminder:

   @username,
   - If you plan to work today, please reply to my messages <message_1_id>, <message_2_id>, <message_3_id>
   - If you don't, send /skip_today

   Here, <message_*_id>-s are messages from today's message that mentioned @username and received no reply.

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Superseded by https://github.com/team-work-tools/team-work-telegram-bot/issues/73 https://github.com/team-work-tools/team-work-telegram-bot/issues/71