dialog:verify should include a --schema option

[chrimc62]

It would be nice for dialog:verify if you could specify a default $schema to use. This would prevent getting lots of errors about their not being a $schema. Should also look at why messages about not being used seem to just use the "last file". For example in the below the unused dialogs are an issue, but ViewToDoDialog has nothing to do with it.

C:\Users\chrimc\source\repos\botbuilder-samples\samples\csharp_dotnetcore\adaptive-dialog\08.todo-bot-luis-qnamaker\generated>bf dialog:verify *.dialog
ViewToDoDialog.lu.dialog - warning DLG005: Unused id Microsoft.LuisRecognizer[LUIS_AddToDoDialog]
ViewToDoDialog.lu.dialog - warning DLG005: Unused id Microsoft.MultiLanguageRecognizer[LUIS_AddToDoDialog]
ViewToDoDialog.lu.dialog - warning DLG005: Unused id Microsoft.LuisRecognizer[LUIS_DeleteToDoDialog]
ViewToDoDialog.lu.dialog - warning DLG005: Unused id Microsoft.MultiLanguageRecognizer[LUIS_DeleteToDoDialog]
ViewToDoDialog.lu.dialog - warning DLG005: Unused id Microsoft.LuisRecognizer[LUIS_GetUserProfileDialog]
ViewToDoDialog.lu.dialog - warning DLG005: Unused id Microsoft.MultiLanguageRecognizer[LUIS_GetUserProfileDialog]
ViewToDoDialog.lu.dialog - warning DLG005: Unused id Microsoft.LuisRecognizer[LUIS_RootDialog]
ViewToDoDialog.lu.dialog - warning DLG005: Unused id Microsoft.MultiLanguageRecognizer[LUIS_RootDialog]
ViewToDoDialog.lu.dialog - warning DLG005: Unused id Microsoft.LuisRecognizer[LUIS_ViewToDoDialog]
ViewToDoDialog.lu.dialog - warning DLG005: Unused id Microsoft.MultiLanguageRecognizer[LUIS_ViewToDoDialog]
10 files processed.
10 found.

[enhancement]