Changes

tsk50 Fixes in explore stories REST and EJB
Removed the parser methods in the Gender and Topic enums in order to
take advantage of the function valueOf that java includes by default.
Default params are now managed with the annotation @DefaultValue in the
explore endpoint, improving code correction. The behavior of the
findStoryById function when an error is encountered has been unified
with the rest of the class. In the REST test class some missing previous
and posterior tests were added and some unnecessary tests were removed. 
Unnecessary imports and incorrect code format corrected.