Merge pull request #3369 from ussuri/small-fixes-3

Fit most of spark.dart into 80-char width
Restrict "Properties" context menu item only to a single selected resource
Revert "Restrict "Properties" context menu item only to a single selected resource"

This reverts commit e02824cb53249b47ac33e606fe8200891fd60b0f.
Merge pull request #3371 from ussuri/small-fixes-3

Don't show "Properties" context menu item when multiple resources are selected
Fix introduced bug + remove unused imports