[frontend] add skeleton loader on main lists (#1409)

[guillaumejparis]

Add skeleton loader on simulations/scenarios/atomic testings lists
Fix issues with filters height & loading in simulation overview

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 32.06%. Comparing base (8834ed8) to head (d3aaaef).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #1841   +/-   ##
=========================================
  Coverage     32.06%   32.06%           
  Complexity     1609     1609           
=========================================
  Files           561      561           
  Lines         16861    16861           
  Branches        984      984           
=========================================
  Hits           5406     5406           
  Misses        11211    11211           
  Partials        244      244           

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