Fixed autocomplete bug for documentation search.js on mobile devices

[smistad]

Fixes issue #196
Detect if browser is on mobile device, and if so skip the appending of autocomplete text.
Detecting mobile browser taken from here: https://stackoverflow.com/questions/11381673/detecting-a-mobile-browser

Should probably just hide the key guide in the search dialog as well on mobile since they are not relevant...?

[codecov]

Codecov Report

Merging #197 (1dd69b8) into master (3a29473) will decrease coverage by 0.10%.
The diff coverage is 53.33%.

@@            Coverage Diff             @@
##           master     #197      +/-   ##
==========================================
- Coverage   98.28%   98.18%   -0.11%     
==========================================
  Files          27       27              
  Lines        6646     6655       +9     
  Branches       44       46       +2     
==========================================
+ Hits         6532     6534       +2     
- Misses        114      121       +7     

Impacted Files	Coverage Δ
documentation/search.js	98.07% <53.33%> (-1.93%)	⬇️

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[mosra]

As mentioned in #196, this got solved in a different way in b598223, with an attempt to restore the autocompletion functionality stashed in #213.