Filter bones

[cochrane]

When you know which bone(s) you want to edit, clicking through the entire tree can be annoying and time-consuming. Some option to search for particular bones would be useful.

Open questions:

• How would the UI look like? Filtering the current list isn't exactly perfect, so maybe a second "search" version of the source list, similar to what Xcode has?
• How do we search? "Contains" seems simple enough, but something like https://radianteld.deviantart.com/journal/XPS-Dress-Bones-A-new-approach-738541602 suggests that regular expressions would be nice as well. Then one could simply search for "dress font left [0-9]+a". Alternatively a search with two fields for "starts" and "ends" would probably be nicer for users who are not familiar with Regexp syntax.

[cochrane]

Stop overthinking the UI, "just" filter everything that is in a list there, including lights, items and meshes (items get shown if anything below them is shown, bones get shown if they or their child is shown, whatever it is gets bolded if it matches directly)