Another model for calculating pricelevel

[jonaz]

we take the max and min value for 24h in the past.

level 1 = if the price is below min plus 20% of the difference between max and min and so on...

fixes #369

[codecov[bot]]

Codecov Report

Merging #398 (b594508) into master (20eca9c) will increase coverage by 0.17%. The diff coverage is 77.96%.

@@            Coverage Diff             @@
##           master     #398      +/-   ##
==========================================
+ Coverage   56.53%   56.70%   +0.17%     
==========================================
  Files          58       58              
  Lines        4385     4428      +43     
==========================================
+ Hits         2479     2511      +32     
- Misses       1668     1676       +8     
- Partials      238      241       +3     

Impacted Files	Coverage Δ
nodes/stampzilla-server/webserver/webserver.go	39.81% <ø> (ø)
nodes/stampzilla-tibber/model.go	62.67% <77.96%> (+3.04%)	:arrow_up: