Composer improvements

[skdw]

This PR solves some problems with the Composer (#8):

• Reverts missing GateGrid hashing
• Fixes the grid scrolling
• Adds some CSS details
• Introduces switching between tabs
• Refactors the controlled gates lines
• Adds the placeholder on the composer loading

[codecov[bot]]

Codecov Report

Merging #79 (1640647) into develop (43bd7a6) will increase coverage by 2.27%. The diff coverage is 97.33%.

@@             Coverage Diff             @@
##           develop      #79      +/-   ##
===========================================
+ Coverage    91.93%   94.21%   +2.27%     
===========================================
  Files           39       40       +1     
  Lines         1042     1071      +29     
===========================================
+ Hits           958     1009      +51     
+ Misses          84       62      -22     

Flag	Coverage Δ
unittests	94.21% <97.33%> (+2.27%)	:arrow_up:

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
Explorer/Components/Composer/Drawing/Line.razor	100.00% <ø> (+25.00%)	:arrow_up:
Explorer/Components/Composer/Gate.razor	88.88% <ø> (+35.55%)	:arrow_up:
Explorer/Components/Composer/Composer.razor	86.79% <89.47%> (+8.53%)	:arrow_up:
Common/GateGrid.cs	97.45% <100.00%> (+0.30%)	:arrow_up:
Common/QuantumGate.cs	58.33% <100.00%> (+3.78%)	:arrow_up:
Explorer/Components/Composer/Grid.razor	89.47% <100.00%> (+14.84%)	:arrow_up:
Explorer/Components/Composer/Grids.razor	100.00% <100.00%> (ø)
... and 1 more

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