set up declarations for every builtin item

Some builtin items that are injected after reading the project
did not have any property declarations. The declarations contain
the default values and we want to use the default values from the
declarations in the next commit.

Preparation for fixing QBS-341.

Change-Id: Ic82375b8bfd9f1c092d2b4d9aab54c70dc866272
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>
fix default value initialization

The default values for properties must be set in the property
declarations to make them available in other properties.
Affected were all condition properties, Group.overrideTags,
Artifact.alwaysUpdated and Rule.multiplex.

Task-number: QBS-341

Change-Id: Ia8d34341c43aed852a858d381ef39b1ba85dbd6e
Reviewed-by: Christian Kandeler <christian.kandeler@digia.com>