Refactoring i-ajax block

 * Added some public functions to control transfered data - add or change any jQuery.ajax params, just override required public function
 * Added simple caching on browser side for specified functions with needed timeout
 * Added tests for new functionality
 * Changed default timeout for requests from 1s up to 25s
 * Removed some duplicated code (jQuery.ajax calls)
 * Fixed error handling on server-side
 * Fixed travis-ci building error
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