SlideImage - implement ImageUploadField

[jsirish]

closes #82

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (1.0@25e010b). Click here to learn what that means.
The diff coverage is 100%.

@@          Coverage Diff           @@
##             1.0      #87   +/-   ##
======================================
  Coverage       ?   64.61%           
======================================
  Files          ?        2           
  Lines          ?      130           
  Branches       ?        0           
======================================
  Hits           ?       84           
  Misses         ?       46           
  Partials       ?        0

Impacted Files	Coverage Δ
code/SlideImage.php	100% <100%> (ø)

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