NEW "Show children as list" tree context action

Allows for easier navigation between tree and list,
particularly if a node has many children nodes
(since it doesn't require expanding that node).

Uses a new 'ss-tabs-force-active' class on the tabset
to enforce the correct view state. This also fixes an issue
where you couldn't link to a list view directly via URL.

Depends on https://github.com/silverstripe/sapphire/pull/1288 being merged in.

![](https://api.monosnap.com/image/download?id=Hj1q1DFQhCidfwhlyNISSRLzw)