Usability enhancements

[vranki]

The bot is not very easy to use for novice users and it could be improved quite easily by doing some small usability enhancements.

Feel free to split to more issues if needed. All should be easy to implement.

• When a previously unknown user starts a chat with the bot, the bot should say something like "I'm the telegram bridge bot. Say !tg login to log in to telegram, or !tg help to list all commands.". Maybe even "Would you like to start login process? (y/n)" and use answer to that instead of !tg login.

• !tg login text is not very clear.
  "If you would like to log in within Matrix, please send your phone number or bot auth token here." <- does this mean just say the phone number or token to the bot or with !tg login parameter?
  I don't know what bot auth token is or why it's needed, remove the mention from the text or explain it.
  IMO logging in via web page should be the preferred way and should be on top.
  Perhaps the text should just be "Open this web page and enter your phone number to continue." and more advanced stuff should be behind another command.

• Login web page: Remove the matrix id field. It's read only and not really needed normally.

• Login web page: "Request code" and "Use bot token" are not easy to understand. I'd change to "Request code" to "Continue". "Use bot token" could be even smaller to avoid confusing users.

• Login web page: "Code requested successfully." -> "Code requested successfully. Look at your telegram messenger and type the 5 number login code you have received to field below."