redbiom nice display of 504

[antgonza]

After doing some more tests with qiita/redbiom, I realized that if you retrieve a lot of results, the server will send a 504 (timeout) and this wasn't being caught by JS. Obviously, this is not a solution but the solution is something that might take some discussion of how to better implement + implementation time. So for the time being this PR adds a "nice" error message.

If timeout:

if something else,

Additionally, decided to improve the show_loading by adding a flag to show some extra text: "This task might take a long time (up to 5 minutes), please do not close this page.". This feature is currently only being used by redbiom but this might be useful for others in the future. Note that 5 min is just a number based on what I was seeing in my tests.

[codecov-io]

Codecov Report

Merging #2311 into release-candidate will not change coverage.
The diff coverage is n/a.

@@                Coverage Diff                @@
##           release-candidate   #2311   +/-   ##
=================================================
  Coverage               93.8%   93.8%           
=================================================
  Files                    163     163           
  Lines                  18581   18581           
=================================================
  Hits                   17430   17430           
  Misses                  1151    1151

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