CDK-445: Allow hive repos to open any Kite table.

This removes the check in load that enforces a managed provider only
opens managed tables, and a similar check in external. The behavior is
tested in TestManagedExternalHandling.

The only change to the repository classes is to move delete into the
abstract repository and make it detect whether the table is external or
managed and use the correct implementation.

This also fixes update, which dropped property updates.
CDK-265: Filter listed Hive tables that are not readable.

This determines whether a table is readable by checking the type and
getting a descriptor for it. That ensures that the table uses supported
input and output formats and that the schema is available.

When converting from a table to a descriptor, HiveUtils now checks
whether the Hive table is partitioned. If so, a partition strategy
expression is requried. This prevents listing tables that can't be read
because they are not partitioned with Kite. In the future, we can
translate from Hive partition columns to a Kite strategy, but because
there is no way to know how the partition columns are derived, they
should be provided partitioners, which is not yet implemented.
CDK-240: Remove key checks when writes are not bounded.

This adds the Constraints#isUnbounded() method from #100 to check
whether the constraints are unbounded and should be ignored.
Added DatasetTarget.toString method.
CDK-281. Push Kite artifacts to maven central

Make the necessary POM changes to push artifacts to
ossrh (http://central.sonatype.org/pages/ossrh-guide.html)
added hasValue check to prevent to get 0 from not set optional int property etc.

added hasValue check to prevent to get 0 from not set optional int property etc.

added hasValue check to prevent to get 0 from not set optional int property etc.
Merge pull request #133 from fiserro/master

kite-morphline-protobuf - added a "hasValue" check
kite-morphlines-protobuf: hasValue check - added corresponding user doc
Merge pull request #134 from fiserro/master

kite-morphlines-protobuf: hasValue check - added corresponding user doc
CDK-332: Deprecate DatasetReader#open and DatasetWriter#open.

This deprecates the reader and writer open methods so that users know
not to use them the design of the readers and writers remains the same,
with an initialization step. But, the initialization is done in an SPI
method, initialize, that is called after the reader or writer is
constructed, but before it is returned from newReader or newWriter.

The code has been moved to the new method by adding open to the
AbstractDatasetReader and a new AbstractDatasetWriter that logs a
warning that the call is no longer required. Tests that called log have
been migrated by either replacing the open call with a call to
initialize, or by removing the call to open. The first case is used
whenever the test instantiates the reader (or writer) itself, as in
TestCSVFileReader, and the latter is used when the reader comes from a
dataset or view.

Some helper methods expected an unopened reader either from newReader or
instantiated directly. These methods now check if the reader is open
and will call initialize if needed.