Fix Dict/Unicode bug

[ilan-gold]

Related to the fix for #3435 we need to actually check types first -as I understand it, if the dict was stored and then is immediately reused, the django model returns a dict while a subsequent call later will return a string when it actually hits the database. Correct me if I'm wrong. In general, it's probably worth migrating to https://docs.djangoproject.com/en/1.9/ref/contrib/postgres/fields/#jsonfield once we have it. Feel free to comment

[codecov]

Codecov Report

Merging #3475 into develop will decrease coverage by 0.02%.
The diff coverage is 50%.

@@             Coverage Diff             @@
##           develop    #3475      +/-   ##
===========================================
- Coverage    87.44%   87.42%   -0.03%     
===========================================
  Files           96       96              
  Lines        16932    14843    -2089     
===========================================
- Hits         14807    12977    -1830     
+ Misses        2125     1866     -259

Impacted Files	Coverage Δ
refinery/tool_manager/models.py	95% <0%> (-0.58%)	⬇️
refinery/core/models.py	82.63% <100%> (-1.11%)	⬇️
...nery/data_set_manager/single_file_column_parser.py	84.61% <0%> (-7.19%)	⬇️
refinery/data_set_manager/views.py	65.72% <0%> (-4.62%)	⬇️
refinery/analysis_manager/tasks.py	72.04% <0%> (-3.29%)	⬇️
refinery/data_set_manager/isa_tab_parser.py	64.87% <0%> (-3.13%)	⬇️
refinery/core/views.py	69.24% <0%> (-2.88%)	⬇️
refinery/file_store/tasks.py	58.37% <0%> (-2.05%)	⬇️
refinery/file_store/utils.py	68.93% <0%> (-1.81%)	⬇️
refinery/tool_manager/views.py	92.3% <0%> (-1.48%)	⬇️
... and 10 more

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[hackdna]

Yes, serialization happens when you call save(): https://docs.djangoproject.com/en/1.8/ref/models/instances/#what-happens-when-you-save
If you make sure the workflow is always read from the DB then checking the value type won't be necessary.