Add warning interval score

[nikosbosse]

Add warning to interval score if the interval range looks wrong as discussed in #277

[codecov]

Codecov Report

Merging #281 (82d6358) into master (aef47ec) will decrease coverage by 0.33%.
The diff coverage is 28.57%.

❗ Current head 82d6358 differs from pull request most recent head 7484bdc. Consider uploading reports for the commit 7484bdc to get more accurate results

@@            Coverage Diff             @@
##           master     #281      +/-   ##
==========================================
- Coverage   90.55%   90.23%   -0.33%     
==========================================
  Files          22       22              
  Lines        1324     1331       +7     
==========================================
+ Hits         1199     1201       +2     
- Misses        125      130       +5     

Impacted Files	Coverage Δ
R/interval_score.R	84.44% <28.57%> (-10.30%)	⬇️

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[seabbs]

This looks good and seems like a sensible check in the first instance whilst we consider redefining as @adrian-lison suggested (that discussion likely needs to be ported to an issue).