The Connector framework now has a way for connector implementations
to handle "extra" properties that are not normally supported by the
external system that the connector is using. These extra properties
can be stored in the same Infinispan cache used to persist the
regular "internal" repository content, although connector implementations
are responsible for explicitly using this new facility.

The file system connector has been changed to take advantage of this
mechanism. By default, all properties that cannot be represented
by native file system attributes (e.g., lastModified, file content,
etc.) are stored using the extra properties facility. However,
the connector can also be configured to store these extra properties
on the file system in "sidecar" files, in the same way that the
file system connector in ModeShape 2.x worked. These sidecar files
can be of several formats, including JSON, BSON, or the ModeShape 2.x
format (a text-based but proprietary format).

Several new tests were added to verify the functionality works as
expected.

…ages

The FileSystemConnector is now in the same 'org.modeshape.connector.filesystem' package as in 2.x, and it
follows the convention used by the sequencers. Note that the file system connector is still located in
the 'modeshape-jcr' module rather than a separate module (as in 2.x) - this is for simplicity.

The MockConnector was moved into the test source, since it is now only used by the test cases
and can be configured like any other connector.

…JavaDoc.