Decrease notification expiration time

[craig-willis]

Reduces event notification expiration time for events that do not require user acknowledgment to 5s. This should resolve the problem identified in whole-tale/ngx-dashboard#139 (comment).

To test:

• As user 1, create and share tale with user 2 with both users actively logged in
• User 1 and user 2 select metadata page in edit mode
• User 1 edits tale metadata and saves, user 2 confirms sync modal appears and selects either yes or no
• Wait 30s
• Sync modal should not reappear

[codecov]

Codecov Report

Merging #457 (9e8250d) into master (fc0f96b) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #457   +/-   ##
=======================================
  Coverage   92.00%   92.00%           
=======================================
  Files          52       52           
  Lines        3929     3929           
=======================================
  Hits         3615     3615           
  Misses        314      314           

Impacted Files	Coverage Δ
server/utils.py	76.92% <100.00%> (ø)

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