Add demo mode to dashboard

[dashby3000]

Adding functionality to suppress "menu" for a "demo" mode. This will allow "pre-sales" to show dashboard in a publicly available app without worry about users starting heap dumps or profiles

[codecov-io]

Codecov Report

Merging #107 into master will increase coverage by 0.07%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##           master     #107      +/-   ##
==========================================
+ Coverage    60.6%   60.68%   +0.07%     
==========================================
  Files           2        2              
  Lines         231      234       +3     
==========================================
+ Hits          140      142       +2     
- Misses         91       92       +1

Impacted Files	Coverage Δ
lib/appmetrics-dash.js	60.51% <66.66%> (+0.08%)	⬆️

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[sjanuary]

@dashby3000 this seems like a good addition. I've renamed this PR as the title wasn't very clear. Will review along with #108.

[sjanuary]

@dashby3000 if you remove the ability to switch profiling on then you should also remove the profiling tab since it's redundant. Alternatively we could keep the menu so that profiling can still be enabled but just remove or disable the NodeReport and HeapDump items.

Also I'm not exactly sure how you created this PR but it wasn't easy for me to test your changes (I actually had to copy and paste from GitHub). In future it would be better to create a public fork and make the pull request from there. I'd like to see this PR combined with the contents of #108 and some new changes to either remove the profiling tab or keep the menu and remove the dump actions, all rolled in to one new PR made from a public fork.

[sjanuary]

Changes needed, as described in comment