Allow templates from non-standard locations to use template.delimiters config option

I need to use templates from non-standard location with non-standard template delimiters. Revel only uses template.delimiters config option for templates from ViewsPath. This PR solves the problem.

I also need a way to insert a hook in between revel.Init and revel.Run, to add paths to the TemplatePaths slice. For now I'm forced to reinstantiate MainTemplateLoader in an OnAppStart hook (this hook runs, alas, after instantiation of the said loader):

```
revel.MainTemplateLoader = revel.NewTemplateLoader([]string{
	filepath.Join(revel.BasePath, "some/path"),
})
revel.MainTemplateLoader.Refresh()
```

This is not very nice. What would you recommend?