DONE: Add command to remove all sheet icons from an app's sheets

[mountaindude]

Is your feature request related to a problem? Please describe.
Would be useful during testing of BSI to quickly remove all existing sheet icons from an app.

[mountaindude]

Design notes

• This command will be added for both QS Cloud and client-managed QS.
• In its first version the command will be a all-or-nothing command, i.e. all sheet icons will be removed from the specified app(s).
• Future versions may offer the possibility to specify that icons should be removed for only some sheets within the specified app(s).