XD-591 Improve build file distribution tasks

Making distZip copy all binary installs into the primary distribution
zip file. This was previously done in zipXD

Making distZip part of Application tasks - overriding description
from application plug-in

Adding distTar as part of Application tasks - overriding description
from application plug-in

Renaming distXD to copyInstall for consistency and making it part of
Application tasks

Changing description of dist, keeping it as the the driving task for
generating all distribution artifacts to be consistent with the build
for Spring Integration
XD-591 Updating README for distribution zip