This commit improves the japicmp integration in the build:

1) Add a finalizedBy task that prints a filtered report

The basic text report uses * and ! as markers for binary and source
incompatible changes respectively. Additionally, a MODIFIED class is
marked with ***. This task attempts at pinpointing the incompatible
changes only in the report, and printing these lines.

This report is called out in the "how to fix" tip in the CI preliminary
step.

2) Ensure sourceModified changes are considered

See reactor/reactor#722.

If a change is binary compatible but not source compatible, using
`onlyBinaryCompatibleModified = true` will mask the issue. This
change uses `onlyModified = true` instead. This is slightly more
verbose, but this is alleviated by (1).

3) Exclude NEW_DEFAULT_METHOD as a whole

Since japicmp-grale-plugin v0.4.1 the new `compatibilityChangeExcludes`
parameter allows us to ignore all occurrences of a default method added
to an interface, instead of having to exclude each such method one by
one.

…wClasspath