all: Comments and cosmetics (#8218)

* lib/api: Note ItemStarted and ItemFinished for default filtering.

The reasoning why LocalChangeDetected and RemoteChangeDetected events
are not included in the event stream by default (without explicit
filter mask requested) also holds for the ItemStarted and ItemFinished
events.  They should be excluded as well when we start to break the
API compatibility for some reason.

* gui: Enumerate unused event types in the eventService.

Define constants for the unused event types as well, for completeness'
sake.  They are intentionally not handled in the GUI currently.

* cmd/syncthing: Harmonize uppercase CLI argument placeholders.

Use ALL-UPPERCASE and connecting dashes to distinguish argument
placeholders from literal argument options (e.g. "cpu" or "heap" for
profiling).  The dash makes it clear which words form a single
argument and where a new argument starts.

This style is already used for the "syncthing cli debug file" command.

* lib/model: Simplify event data structure.

Using map[string]interface{} is not necessary when all values are
known to be strings.

cmd/syncthing/cli/errors.go

@@ -27,7 +27,7 @@ var errorsCommand = cli.Command{
 		{
 			Name:      "push",
 			Usage:     "Push an error to active clients",
-			ArgsUsage: "[error message]",
+			ArgsUsage: "ERROR-MESSAGE",
 			Action:    expects(1, errorsPush),
 		},
 		{

cmd/syncthing/cli/operations.go

@@ -39,13 +39,13 @@ var operationCommand = cli.Command{
 		{
 			Name:      "folder-override",
 			Usage:     "Override changes on folder (remote for sendonly, local for receiveonly). WARNING: Destructive - deletes/changes your data.",
-			ArgsUsage: "[folder id]",
+			ArgsUsage: "FOLDER-ID",
 			Action:    expects(1, foldersOverride),
 		},
 		{
 			Name:      "default-ignores",
 			Usage:     "Set the default ignores (config) from a file",
-			ArgsUsage: "path",
+			ArgsUsage: "PATH",
 			Action:    expects(1, setDefaultIgnores),
 		},
 	},