implemented for caching the laterpay_post_teaser as default

* implemented for caching the laterpay_post_teaser as default
* added nonces to purchased post and statistic tab ajax
* renamend LaterPay_Controller_Post_Content to LaterPay_Controller_Post
* added new lpVars for better JS-handling
* added "use strict"; to js
* jslint check

references to issue: #258
thats fine, we return nothing on ajax requests, on success it returns full html, so its difficulty to return an json-error or something like that.