Add HierarchyRepeater

[cafour]

There is currently no control in the framework able to render recursive hierarchies, so I backported HierarchyRepeater from business pack over here.

Implementing any ItemsControl, let alone a repeater, is a mine field, so any feedback is very, very welcome.

[quigamdev]

We need to rewrite this code to use the standard Item Template mechanism as Repeater uses.
Tbh we should completely rewrite this control.

[cafour]

@quigamdev

We need to rewrite this code to use the standard Item Template mechanism as Repeater uses.

What do you mean by standard item template mechanism? This control already uses the same mechanism as Repeater with the exception of the ResourceManager.AddTemplateResource method.

This method cannot be used since it generates the template id based on the hash of template's contents... which needs to contain the template id. This can be overcome in two ways: either by rendering the template twice -- once to obtain the id and once to put the id back in, or by generating the template id in some other way (as I did in this PR).

Tbh we should completely rewrite this control.

This is already pretty much a complete rewrite of bp:HierarchyRepeater. I'd rather fix this implementation than start all over again.

[quigamdev]

It looks good to me. I have found just minor issues.
It would be nice to have also some perf test.

[quigamdev]

I have just noticed that unit tests are failing.

[cafour]

Limitation: ItemWrapperCapability cannot have bindings with a data context set to the item. This limitation is cause by the need to have consistent date context nesting both in client-rendering and server-rendering.