Use heroku-shields instead of heroku-badge

[CasperWA]

We can now add a logo to the badge and still have testing of whether heroku is up or not.

Might as well update this as well 😄

The heroku instance we usually use to get the badge is down and is quite rigid. This new one is up and let's us use shield.io better. The new one is using this.

It looks thus:

[codecov]

Codecov Report

Merging #284 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #284   +/-   ##
=======================================
  Coverage   90.03%   90.03%           
=======================================
  Files          54       54           
  Lines        2269     2269           
=======================================
  Hits         2043     2043           
  Misses        226      226           

Flag	Coverage Δ
#unittests	90.03% <ø> (ø)

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