CrossBucket push, frontend

[fiskus]

• CopyButton is an action button and bucket successor's select
• CopyPackageDialog is copy-pasted from Create and Update dialog
• I've split DialogForm into several components we can reuse for Update, Create and Copy dialogs. I suspect, there will be PushDirectory dialog
• I've added some snapshot tests for small components

Hierarchy for new components:

PackageTree
 +- CopyButton
       "click" -> BucketsListFetcher 
                   +- Menu

 +- PackageCopyDialog
   +- PackageDialog.Error
   +- PackageDialog.Success
   +- PackageDialog.Loading
   +- DialogForm
       +- FilesInput -> Dropzone
                         +- Dropzone.Header
                         +- Dropzone.FileEntry[]
                         +- Dropzone.DropMessage
                        Dropzone.Overlay

[codecov-io]

Codecov Report

Merging #1932 (dbd68c3) into master (e22cdcc) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1932   +/-   ##
=======================================
  Coverage   90.40%   90.40%           
=======================================
  Files          64       64           
  Lines        7792     7792           
=======================================
  Hits         7044     7044           
  Misses        748      748           

Flag	Coverage Δ
api-python	89.35% <ø> (ø)
lambda	92.40% <ø> (ø)

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[nl0]

there's a possible bug related to error handling and async / await in onSubmit / requestPackageCopy, the rest looks good