The xxf:default MIP

All,

As discussed in today's call, we have a "MIP" similar to `calculate` which
we called `xxf:default`:

    https://doc.orbeon.com/xforms/core/binds#the-xxf-default-mip

There is also support to force re-evaluation with `<xf:recalculate>` and
`<xf:insert>`:


https://doc.orbeon.com/xforms/actions/repeat-insert-delete#evaluation-of-initial-values-upon-insert

-Erik