Add JUnit tests for JsonArray Class

[Phhofm]

Added tests so that class-coverage is 100%

Before:

Now:

[lyubomyr-shaydariv]

1. It would be nice to have your branches rebased onto the latest upstream branches (the master is currently at 49d8630).
2. Also, it would be very nice to have the whitespaces preserved:
   • git diff --stat Phhofm/jsonarray_testcoverage~1..Phhofm/jsonarray_testcoverage currently produces 1 file changed, 357 insertions(+), 74 deletions(-)
   • but git diff --stat --ignore-all-space Phhofm/jsonarray_testcoverage~1..Phhofm/jsonarray_testcoverage produces 1 file changed, 285 insertions(+), 2 deletions(-)

[eamonnmcmanus]

@Phhofm, if you're still interested in making this change, can you sign the CLA? (I'm not sure why the system said that you had and then that you hadn't.)

[Phhofm]

@Phhofm, if you're still interested in making this change, can you sign the CLA? (I'm not sure why the system said that you had and then that you hadn't.)

Done, CLA check passed now :)

[eamonnmcmanus]

Thanks!