Support slash commands on Telegram

[fabioxgn]

Telegram bots by default run in "privacy mode" which only passes commands starting with a forward slash / to bots.

Right now the bot to run on telegram needs privacy mode off, but this is easy fixed just changing the prefix for commands on telegram to /.

[doenietzomoeilijk]

I've just created a PR that would enable this, since the parse() function can now tell a message is coming from Telegram, and modify the prefix accordingly.