Re-enable QmlProjectManager by default

Acting on user feedback.

This essentially reverts commit 7e8fb3a9e9,
but demotes the wizards from "Application" to "Project" and adds
a tooltip in the hope to make "accidental" use less likely.

Change-Id: I385bcfc5cdcb9bb3c36f9168a7fc6480f4fc5062
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@theqtcompany.com>
Reviewed-by: Eike Ziller <eike.ziller@theqtcompany.com>
Reviewed-by: Kai Koehne <kai.koehne@theqtcompany.com>

src/plugins/qmlprojectmanager/QmlProjectManager.json.in

@@ -2,7 +2,6 @@
     \"Name\" : \"QmlProjectManager\",
     \"Version\" : \"$$QTCREATOR_VERSION\",
     \"CompatVersion\" : \"$$QTCREATOR_COMPAT_VERSION\",
-    \"DisabledByDefault\" : true,
     \"Vendor\" : \"The Qt Company Ltd\",
     \"Copyright\" : \"(C) 2015 The Qt Company Ltd\",
     \"License\" : [ \"Commercial Usage\",