Deployment will be handled by ASF's Jenkins instances which trigger
the deployment of snapshot versions every night. This way, we have not
only separated deployment from CI testing, but also improved the
reliability of the test and deployment infrastructure.

- remove Travis dependency from Maven deploy script

- set force-dependency version to Flink version

This assures deployment works when only credentials for the snapshot
deployment are available. Previously, we deployed snapshots with release
credentials. These credentials would be over-privileged.

- remove old credentials from Travis config file

This closes #1619.

[FLINK-3550] [examples] Rework WindowJoin to properly demonstrate continuous window joins (Java + Scala)

This closes #1759

This closes #1711

[FLINK-3491] [tests] Prevent URIException in HDFSCopyTest and disable HDFSCopyUtilitiesTest on Windows

This closes #1703

This closes #1760

This closes #1756

This closes #1763

This also consolidates the various wrapper classes for fold() and reduce() functions.

This closes #1765

The ConnectionUtils.findAddressUsingStrategy method tries to find out the local address which is
accessible by other machines of the cluster. It tries to connect to a specified address to do so.
In case that the no connection could be established, it uses an heuristic. Before it randomly
picked a NetworkInterface which is bound to an Inet4Address, not a loop back address and not a
link local address. In most cases it makes more sense to default to the
InetAddress.getLocalHost() address instead. This PR replaces the old heuristic with simply
returning the InetAddress.getLocalHost(). This of course requires that the system on which Flink
is running, is properly configured.

This closes #1758.

This closes #1664.

This closes #1710.

This ensures that all properties of the root pom are properly
resolved by running the Shade plugin. Thus, our root pom does not have
to depend on a Scala version just because it holds the Scala version
properties.

This closes #1755

Closes #1685

This closes #1744

This closes #1750

The fold API call takes an initial value as well as a fold function. In Scala it is possible
to provide an anonymous function. In order to easily support multi line anonymous functions
as well as being consistent with Scala's collection API, this PR adds another parameter list
to the fold API call, which contains the fold function parameter.

Insert spaces between first parameter list and curly braces of anonymous function

This closes #1748.

This closes #1751.

This closes #1749.

This closes #1743

This closes #1737

This brings it more in line with *ProcessingTimeWindows and makes it
clear what type of window assigner it is.

The old name, i.e. SlidingTimeWindows and TumblingTimeWindows is still
available but deprecated.

This enforces that the user always has to specify keys for both inputs
before .window() can be called.

This closes #1732.

This closes #1735.