PLT-4938 Add app package and move logic over from api package (#4931)

* Add app package and move logic over from api package

* Change app package functions to return errors

* Move non-api tests into app package

* Fix merge

cmd/platform/mattermost.go

@@ -9,7 +9,7 @@ import (
 	"fmt"
 	"os"
 
-	"github.com/mattermost/platform/api"
+	"github.com/mattermost/platform/app"
 	"github.com/spf13/cobra"
 
 	// Plugins
@@ -79,7 +79,7 @@ func resetCmdF(cmd *cobra.Command, args []string) error {
 		}
 	}
 
-	api.Srv.Store.DropAllTables()
+	app.Srv.Store.DropAllTables()
 	CommandPrettyPrintln("Database sucessfully reset")
 
 	return nil