Update AlitheiaCore

[mkechagia]

-Check AlitheiaCore on Java 7
-Update OSGi

[eligu]

@mkechagia
It would be nice if you check AC with the default settings running on a new fresh install MySQL installation (the latest one, just change the pom.xml to be sure to use MySQL). As I stated in a previous version I experienced some issues
but @gousiosg was pretty sure there is not any problem with MySQL. If you confirm (by checking/testing) that there isn't any problem with MySQL, at least update the documents, on how to properly use it, because it means that
given the current documents we weren't unable to use MySQL without experiencing any issue.

MySQL is handy when it comes to testing, given the wide support it has and the tools it has. After running some
metrics, we can compare the stored results in DB (check the tables/records) using visual tools. We can't make this
tests without running AC and calling its API to read the DB in case there is the built in H2 (it is unclear to us where
the DB is stored and how to load it externally).