Suppressed exceptions when updating the index.

The motivation is that when a new page is created, the second of two
update operations may fail, which means that the index document's last
link becomes stale. The system is still 'almost consistent' in the sense
that all other links point to correct documents, apart from the last link
in the index document. This link points to an existing document, but that
document is no longer the most recent document.

However, if the update operation of the index throws an exception, a
client may interpret that as a failure to write an event to storage, and
thus may retry the operation. This would be an error, because the event
has been written, and thus, a duplicate event would be written if the
operation is retried.

For that reason, while the first update operation (of the new previous
page) must succeed or throw an exception, the second update (of the index
page) must silently fail if an error occurs.
Suppressed exceptions when correcting last link

on index. Motivation is the same as in the previous commit.

However, the catch expression is too universal, because when the index is
initially created, the failure of creating the index (instead of updating
it) should still throw an exception.
Allowed exception to be thrown when creating index

because while an index update is non-critical, and should be allowed to
fail, creation of an index is critical. If the index never gets created,
the event stream will not be available.

This, and the two previous commits, resolve #96
(https://github.com/GreanTech/AtomEventStore/issues/96).
Renamed a test method,

in order to make it a bit clearer, what was being tested.
Demonstrated repeated index update failures.

The expanded test cases demonstrate that even if the update of the index
document repeatedly fails, events are still correctly written.
Demonstrated repeated index update failure

within a single page. After updating the test method, I disabled the
exception suppression in the SUT, ran the updated test cases, and verified
that all the test cases still fail.