WTF-748 Fixes and improves module templating (#786)

Fixes and improves the module templating for creating new bare-bones
text widgets.

This command:

    WTF_WIDGET_NAME=MyNewWidget go generate -run=text

now properly generates:

    * the module directory in the /modules directory
    * the widget.go file
    * the settings.go file

with no linter warnings or errors.

Signed-off-by: Chris Cummer <chriscummer@me.com>

generator/settings.tpl

@@ -0,0 +1,29 @@
+package {{(Lower .Name)}}
+
+import (
+	"github.com/olebedev/config"
+	"github.com/wtfutil/wtf/cfg"
+)
+
+const (
+	defaultFocusable = false
+	defaultTitle     = "{{(.Name)}}"
+)
+
+// Settings defines the configuration properties for this module
+type Settings struct {
+	common *cfg.Common
+
+    // Define your settings attributes here
+}
+
+// NewSettingsFromYAML creates a new settings instance from a YAML config block
+func NewSettingsFromYAML(name string, ymlConfig *config.Config, globalConfig *config.Config) *Settings {
+	settings := Settings{
+        common: cfg.NewCommonSettingsFromModule(name, defaultTitle, defaultFocusable, ymlConfig, globalConfig),
+
+        // Configure your settings attributes here. See http://github.com/olebedev/config for type details
+	}
+
+	return &settings
+}