Scope Explosion: Support different messenger platforms

[LinqLover]

Currently, this repository can be only used to built bots for Telegram. However, parts of the message handling and the framework could be reused for other platforms as well. We could expand the scope of this project by renaming it into Bot and providing access to multiple platforms.

This would require some general design changes:

• Mediation/fallback code for features that are not supported on all platforms (e.g. sound messages)
• Message object layer instead of JsonObjects for incoming messages
• Separate message processing logic from message handling logic by extract the former into platform-specific classes (this would also improve the mocking in TelegramSmalltalkBotTest significantly)

Possible platforms to support:

• E-mail?
• Discord?
• Slack?
• Twitter?
• GitHub?