Use TemplateLoader to load ftl templates

Freemarker provides a mechanism to load templates from different sources named Template Loaders. Basically can be used URLTemplateLoader and ClassTemplateLoader to achieve the same behaviour provided in AbstractFormDispatcher but it gives an important feature to make possible to import different templates. For example:
<#import "common_task.ftl" as common/>
<@common.tasktemplate/>

This feature improve template reusability and use of generic macros.

Some other features can be achieved as template caching.