Dataverse External Tools integration

[Xarthisius]

This PR creates a simple endpoint that accepts requests coming from Dataverse external tools and return 303 to a proper dashboard route with an encoded datafile information.

Suggested test:

1. Run girder with env DASHBOARD_URL set to your dashboard instance (needs Data import dashboard#287 and Add support for ingesting data from Dataverse. Fixes #179 #175)
2. Run a dataverse with a ext tool integration pointing to <your_girder>/api/v1/integration/dataverse (remember to set DATAVERSE_URL in wholetale plugin's config)
3. See the magic happen!

[codecov]

Codecov Report

Merging #180 into master will increase coverage by 0.24%.
The diff coverage is 97.43%.

@@            Coverage Diff             @@
##           master     #180      +/-   ##
==========================================
+ Coverage   84.61%   84.86%   +0.24%     
==========================================
  Files          32       34       +2     
  Lines        2022     2061      +39     
==========================================
+ Hits         1711     1749      +38     
- Misses        311      312       +1

Impacted Files	Coverage Δ
server/rest/integration.py	100% <100%> (ø)
server/__init__.py	86.46% <100%> (+0.11%)	⬆️
server/lib/dataverse/integration.py	96.66% <96.66%> (ø)

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