Tweaked pom.xml

Tweaked pom.xml in order to:
 * fix jdk version tio 1.7
 * include junit for unit testing
Added some unit tests for StationStore

Added unit tests to verify the behaviour of the getStation method when
it is fed:
 * a negative station id
 * a station equal to 0
Fixed Station initialization at parsing

Fixed Station initialization at parsing in order to avoid crashes when
trying to handle a response that with one of the expected fields.

The Station is now initialized with default values for its attributes:
 * 0 for all integers
 * null for all Objects
Added lastUpdate field value retrieval

Added lastUpdate field value retrieval in the parsing process.