Allow server-side pagination

Created factory 'ajaxItems' to mantain item count from ajax call.
Updated directive to allow 'showLastPageIfNotExists' parameter to be received.
Updated constant 'paginationConfig' to set the default value of 'showLastPageIfNotExists'
Updated 'totalPages'.
Updated 'totalItems':
  - It works with ajax collections, if the ajax collection size changes between state or view changes, the function will check and update.
  - Added functionality for when your page asked doesn't exist, by default it'll return the user to the last page based on the size of your array. If you set it to false, then you'll be shown the page with no info but a functional pagination bar.