Add a button to shuffle files in a page

[jaidevd]

When viewing a large directory of files, especially if they relate to some computer vision problem, the images often need to be eyeballed randomly. This PR adds a button to shuffle files within a page.

[codecov-io]

Codecov Report

Merging #20 into master will decrease coverage by 0.33%. The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #20      +/-   ##
==========================================
- Coverage   88.25%   87.91%   -0.34%     
==========================================
  Files           9        9              
  Lines        1583     1589       +6     
  Branches      276      276              
==========================================
  Hits         1397     1397              
- Misses        119      125       +6     
  Partials       67       67

Impacted Files	Coverage Δ
vixen/vixen.py	88.14% <100%> (-0.26%)	:arrow_down:
vixen/ui_utils.py	23.07% <0%> (-2.57%)	:arrow_down:
vixen/project.py	91.1% <0%> (-0.6%)	:arrow_down:

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[jaidevd]

@prabhuramachandran I cannot reproduce the build error here Do you have any suggestions?

[prabhuramachandran]

Thanks and sincere apologies for the delayed merge!