Remove distinction between 'Essentials' and 'Addons' in packages

The Qt installer differentiates between "Qt Essentials" and "Qt Addons".

However, as seen in QTBUG-33121 only installing Qt Essentials leaves QtWebkit and other tools broken. This is not necessary a bug: The differentiation between Essentials and Addons is primarily about what a platform has to deliver, not a runtime decision.

Since the differentiation is therefore of limited use, and actually complicates the build & packaging process, I suggest to drop it, and only offer one package, both for binaries and sources.

(Depending on the nature of an addon it might be still offered separately, see e.g. cloud.io and charts.)