Add error handling to node_helper startup sequence

[rejas]

Fixes #2944

Also splits the Server js into a constrcutor and an open call to remove one callback parameter :-)

[codecov-commenter]

Codecov Report

Merging #2945 (86cba45) into develop (7bbf8c1) will decrease coverage by 0.52%.
The diff coverage is 58.33%.

@@             Coverage Diff             @@
##           develop    #2945      +/-   ##
===========================================
- Coverage    64.06%   63.54%   -0.53%     
===========================================
  Files            9        9              
  Lines          295      299       +4     
===========================================
+ Hits           189      190       +1     
- Misses         106      109       +3     

Impacted Files	Coverage Δ
js/server.js	66.21% <56.89%> (ø)
js/app.js	59.20% <64.28%> (-1.14%)	⬇️

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[khassel]

"never merge your own PR" ...

[rejas]

wups :-(

[rejas]

will be more patient with my weather refactor branch, I promise!

[khassel]

tell me if you want to wait for more approvals there or if I should merge ...

[rejas]

Since that (#2849) is quite large, the more eyes the better (looking at @sdetweil @MichMich and maybe @buxxi too for reviews of it)