Add initial support for MVC namespace view resolution config

<mvc:view-resolution /> now allows to configure easily
view resolvers.

Issue: SPR-7093
Make Tiles 3 the default implementation in spring-webmvc

Move spring-webmvc-tiles3 content to spring-webmvc, and
create a spring-webmvc-tiles2 module with Tiles 2 support.

Its allows View Resolution to configure Tiles 3 instead of Tiles 2.

Issue: SPR-7093
Support Java and MVC namespace view resolution config

This commit improves and completes the initial MVC namespace
view resolution implementation. ContentNegotiatingViewResolver
registration is now also supported.

Java Config view resolution support has been added.
FreeMarker, Velocity and Tiles view configurers are registered
depending on the classpath thanks to an ImportSelector.

For both, a default configuration is provided and documented.

Issue: SPR-7093
Introduce Freemarker/Velocity/TilesWebMvcConfigurer

This change improves the support for auto-registration of FreeMarker,
Velocity, and Tiles configuration.

The configuration is now conditional not only based on the classpath
but also based on whether a FreeMarkerConfigurer for example is already
present in the configuration.

This change also introduces FreeMarker~, Velocity~, and
TilesWebMvcConfigurer interfaces for customizing each view technology.

The WebMvcConfigurer can still be used to configure all view resolvers
centrally (including FreeMarker, Velocity, and Tiles) without some
default conifguration, i.e. without the need to use the new
~WebMvcConfigurer interfaces until customizations are required.

Issue: SPR-7093
Update ViewResolver registration classes

Following the separation of FreeMarker/Velocity/TilesConfigurer-related
configuration via separate interface, simplify and streamline the
view registration helper classes which no longer have much difference
(most are UrlBasedViewResolver's).

Updates to Javadoc and tests.

Issue: SPR-7093
Update view-resolver namespace

Issue: SPR-7093