This commit enables compatibility build against Spring Framework 5.

The Velocity and Guava support that are deprecated in the 1.x line have
been removed and few other classes contain minor change to comply to non
backward compatible changes in Spring Framework 5.

This commit also switches the required java version to 8.

Closes gh-6977

See gh-6971
See gh-6973

See gh-6971

This code removes code deprecated in 1.4 with the exception of code that
requires an update to Spring Framework 5.

Closes gh-6971

Remove setResolvePlaceholders() from PropertySourcesPropertyValues
and instead rely only on the constructor.

See gh-6964

Closes gh-6627

Closes gh-6956

Previously, when a Tomcat connector failed to start it was assumed that
the failure was due to the port being in use and a PortInUseException
was thrown. Unfortunately, this assumption doesn’t always hold true.
For example, a Tomcat connector will also fail to start when its using
SSL and the key store password is wrong. This could lead to incorrect
guidance from the PortInUseFailureAnalyzer indicating that a port clash
had occurred when, in fact, it was the SSL configuration that needed to
be corrected.

Unfortunately, Tomcat only tells us that the connector failed to start.
It doesn’t provide access to the exception that would allow us to
determine why it failed to start. This commit updates the embedded
Tomcat container to throw a ConnectorStartFailedException in the event
of a connector failing to start. A new failure analyser,
ConnectorStartFailureAnalyzer, has been introduced to analyse the new
exception and offer some more general guidance.

Closes gh-6896

Closes gh-6583

The default behaviour is unchanged, but it is useful for some applications to be
able to bind without placeholder resolution (e.g. to prevent exposing system
environment variables, if the bound object is being sent over the wire).

Closes gh-6944

See gh-6956

See gh-6956

Closes gh-6951

Closes gh-6949

Closes gh-6948

Closes gh-6947

Closes gh-6946

Closes gh-6945

Closes gh-6944

Closes gh-6943

Closes gh-6942