Adds Image support for Telegram

[FabioRosado]

Description

This is a work in progress. I am raising this PR because I need help with the tests. I spent the whole day trying to go around with it but I couldn't figure out how to go around it.

I am going to try and work on the other connectors after I figure out how to test the telegram connector properly since most other connectors use the API to get and send messages I might have to reuse this code elsewhere.

Status

READY | UNDER DEVELOPMENT | ON HOLD

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration.

• Travis - all green
• Send image to telegram - worked as expected

Checklist:

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation (if applicable)
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[codecov]

Codecov Report

Merging #929 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #929   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files          37     37           
  Lines        2338   2346    +8     
=====================================
+ Hits         2338   2346    +8

Impacted Files	Coverage Δ
opsdroid/connector/telegram/__init__.py	100% <100%> (ø)	⬆️

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[jacobtomlinson]

Thanks for this looks good!