Feature/2180/nextflow dag buttons

[garyluu]

For dockstore/dockstore#2180
which fixes the controls by putting them in its own div under the possible warnings
Also:

• remove cwlviewer expand styles because the dag.component does the expanding now
• gave WDL workflows the possible "DAG cannot be created because some required tools are missing from Github repo" alert
• only show warning alerts if there actually is no dagResults
• guard against no files in wdl-viewer (if the files endpoint errors out, it should not be in a continuous loading state)

[codecov]

Codecov Report

Merging #573 into develop will decrease coverage by 0.02%.
The diff coverage is 22.22%.

@@             Coverage Diff             @@
##           develop     #573      +/-   ##
===========================================
- Coverage    61.73%   61.71%   -0.03%     
===========================================
  Files          232      232              
  Lines         7067     7070       +3     
  Branches       693      693              
===========================================
  Hits          4363     4363              
- Misses        2534     2537       +3     
  Partials       170      170

Impacted Files	Coverage Δ
...pp/workflow/dag/wdl-viewer/wdl-viewer.component.ts	53.44% <22.22%> (-2.92%)	⬇️

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