Show full name if DefaultShowFullName setting activated (#6710)

Adds a new key DEFAULT_SHOW_FULL_NAME (default false) to the [ui] section.
If enabled the full name will be shown (unless it's empty, then
the default username will be used)

modules/templates/helper.go

@@ -63,6 +63,9 @@ func NewFuncMap() []template.FuncMap {
 		"DisableGravatar": func() bool {
 			return setting.DisableGravatar
 		},
+		"DefaultShowFullName": func() bool {
+			return setting.UI.DefaultShowFullName
+		},
 		"ShowFooterTemplateLoadTime": func() bool {
 			return setting.ShowFooterTemplateLoadTime
 		},