changes to make the graphstore ready for JDK11

[seinecle]

• source and compile info changed to JDK11.

• added a module-info

• updated plugin versions

• removed the animal sniffer plugin as it becomes unecessary since the JDK9 (removal of the JRE). See this issue.

• removed the dependency to joda-time, replaced it with java.time classes. This caused a number of changes to make in the parsing / printing logic of dates, since java.time classes don't handle timezone offsets exactly like joda. The Seralization class has also been modified to serialize the ZoneId, instead of the joda-time equivalent.

• tests: almost all tests pass. The ones that don't pass are those which I considered to be cases where the user would provide incorrect date formats. It would be too complex to add the code to handle these user errors. An exception should be raised, it is fine. Example: "2015-01" (when "2015-01-01" is expected) should not be an accepted date format, so the test for it is not useful. 2 or 3 tests like this have been removed (not deleted, just commented out with additional comment as to why).

[eduramiba]

Thank you Clement!

[eduramiba]

Closing old PR