dynamic widget based dashboard

[AnalogJ]

• updating gridstack version. Better Widget UI/UX.
• widgets are initialized dynamically based on JSON
• chart queries are defined dynamically based on JSON
• update chartsjs and ng-charts version
• use raw objects + chartjs parsing key to display data in charts.
• added loading and empty state UI for widgets

closes #156
closes #21

[codecov-commenter]

Codecov Report

❗ No coverage uploaded for pull request base (sandbox@2681df8). Click here to learn what that means.
Patch has no changes to coverable lines.

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Additional details and impacted files

@@            Coverage Diff             @@
##             sandbox     #157   +/-   ##
==========================================
  Coverage           ?   28.09%           
==========================================
  Files              ?      162           
  Lines              ?     4805           
  Branches           ?      452           
==========================================
  Hits               ?     1350           
  Misses             ?     3395           
  Partials           ?       60           

Flag	Coverage Δ
unittests	28.09% <0.00%> (?)

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