Start SMEE client if WEBPROXY_URL is set

[sodre]

Start smee-client if the WEBHOOK_PROXY environment variable is set

ref: #8

[codecov]

Codecov Report

Merging #13 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #13   +/-   ##
=======================================
  Coverage   94.28%   94.28%           
=======================================
  Files           2        2           
  Lines          35       35           
=======================================
  Hits           33       33           
  Misses          2        2           

Impacted Files	Coverage Δ
tests/smee/__init__.py	93.75% <ø> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 711fb5f...01a036a. Read the comment docs.