Add demo mode to dashboard (part 2)

[dashby3000]

Adding a demo option to allow being able to show the dashboard publicly (from demos) without worry of giving the ability to start HEAP dumps or Profiling.

[codecov-io]

Codecov Report

Merging #108 into master will decrease coverage by 0.86%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #108      +/-   ##
==========================================
- Coverage    60.6%   59.74%   -0.87%     
==========================================
  Files           2        2              
  Lines         231      231              
==========================================
- Hits          140      138       -2     
- Misses         91       93       +2

Impacted Files	Coverage Δ
lib/appmetrics-dash.js	59.56% <0%> (-0.87%)	⬇️

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[sjanuary]

Needs changes as described in #107. Should be combined into 1 PR.