add navbar links to Incidents and Field Reports

[srabraham]

This makes it much easier to navigate around IMS.
These links will style badly if the event name is very long, but there's no problem at all for 4-character names, which are all that really matter.

This commit also makes a few other minor style tweaks.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 69.97%. Comparing base (6bb671e) to head (e8a3e19).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...ement/incident/report_template/_report_template.py	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1580      +/-   ##
==========================================
+ Coverage   69.96%   69.97%   +0.01%     
==========================================
  Files         186      186              
  Lines        9235     9236       +1     
  Branches     1492     1492              
==========================================
+ Hits         6461     6463       +2     
  Misses       2661     2661              
+ Partials      113      112       -1     

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