This interceptor creates the HttpSession if it doesn't exist, also SessionMap is recreated and put in ServletActionContext.
This is particular useful when using the <@s.token> tag in freemarker templates.
The tag
do require that a HttpSession is already created since freemarker commits
the response to the client immediately.
Interceptor parameters:
Example:
<action name="someAction" class="com.examples.SomeAction">
<interceptor-ref name="createSession"/>
<interceptor-ref name="defaultStack"/>
<result name="input">input_with_token_tag.ftl</result>
</action>