Changes

tsk15 Corrects the methods exploreStories and calculateNumPagesExplore
Modifies the exploreStories method to use TypedQuery's setMaxResults and 
setFirstResults methods when getting the stories corresponding to each
page
Modifies the calculateNumPagesExplore method to use a specific query to
count the number of items (COUNT query)

tsk15 Add more tests for story exploration
Add more tests to check different combinations to obtain the number of
pages according to the options chosen in the filter (genre, topic and
publication)

tsk34 Fixes getStoriesByUser and calculateNumPagesStoriesByUser methods
Modifies the getStoriesByUser method to use TypedQuery's setMaxResults
and setFirstResults methods when getting the corresponding stories for
pagination
Modifies the calculateNumPagesStoriesByUser method to use a specific
query to count the number of items (COUNT query)

fix: Fixes the searchStories and calculateNumPagesSearch methods
Modifies the searchStories method to use TypedQuery's setMaxResults and 
setFirstResults methods when retrieving stories taking pagination into
account
Modifies the calculateNumPagesSearch method to use a specific query to
count the number of items (COUNT query)