Make image previews actually work

[ThomasJClark]

Fixes #478

[codecov-io]

Current coverage is 53.65%

Merging #480 into master will increase coverage by +0.03% as of 5f105af

@@            master    #480   diff @@
======================================
  Files          130     130       
  Stmts         3866    3867     +1
  Branches       421     421       
  Methods          0       0       
======================================
+ Hit           2073    2075     +2
+ Partial        117     113     -4
- Missed        1676    1679     +3

Review entire Coverage Diff as of 5f105af

---

Uncovered Suggestions

1. +0.55% via .../ExceptionAlert.java#83...103
2. +0.39% via ...cketPreviewView.java#88...102
3. +0.39% via ...indowController.java#219...233
4. See 7 more...

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