build.gradle: standardize dependency specifications code style
build.gradle: standardize dependency specifications code style

There are different styles of specifying dependencies in the
build.gradle file, so let's standardize all of them into one single
style.

This style is chosen as it makes the groupId, artifactId, and version of
the dependency obvious.

Rather than defining the dependency versions as project.ext properties,
just define them directly in the dependencies block so that the
dependency version number is immediately obvious. An exception is made
for the testfx dependencies since their version numbers are shared --
use a local variable (since its only locally used) to define that
instead.

damithc/addressbook-level4,se-edu/addressbook-level3,damithc/addressbook-level4,damithc/addressbook-level4