Add @WebIntegrationTest

[philwebb]

Ideally we would update @IntegrationTest to use the new @BootstrapWith system rather than a custom listener. Unfortunately we can' currently do this due to the fact that @IntegrationTest is used with @WebAppConfiguration and only one @BootstrapWith annotation is respected (see #1956 for background).

We can however introduce a new annotation.

[philwebb]

The main reason for introducing this in 1.2.1 is to provide TestNG support.