XForms Status Update

Checked in last week:
* <setindex> and repeat-index (#278209)
NB. <insert> and <delete> does not set the repeat-index properly (#282828), and repeat-index is an attribute not a pseudo-element (#271724).

* hasFeature(), so now it's possible to figure out that we are present :) (#279021)

* two issues regarding external instances, which now work much better (#279021, #282351)

* submission has improved. It now disables the submit button while submitting (#280312) and removes irrelevant data (#280264).

Coming up:
* one of the many <select> bugs (#278277, #281668, #279063, #282840)

* implementation of index() function (#282777)

* input checkbox behaviour (#273428)

* misc. internal fixes to the MDG (#278368, #278369)

* the XPath dependency calculation really needs to move to Transformiix (#265212)

* support for complex schemas, and other schema stuff

* figuring out why we still have problems with binding to external instance data in some cases

* and possibly we have a volunteer for looking into the UI rendering of some of the data types like date picker

I think the implementation is closing in on a "usable state". The biggest issue wrt. compatibility with other processors is styling. We need support for the pseudo-classes (#271720) and pseudo-elements (#271724). But it mostly needs to be solved outside our little "XForms extension pond" :)