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
I guess my below comment goes for this instance of `exit` as well