update MetaSearch to 0.3.1
remove code
merge back ef0e7d09168d43b0529a1f819108a4741c7e9e75
Fix #11126 (Make up/down buttons work also for layer tree nodes)
Fix QgsLayerTreeModel naming conventions and update Python bindings

I was using a mixture of terms 'symbology items' and 'legend nodes' for the same thing which was confusing
Fix potential crash when adding a group
Merge pull request #1575 from geopython/MetaSearch-0.3.1

Meta search 0.3.1
Start of doxygen page about API breaks
Do not create collaboration diagrams in doxygen docs

The diagrams do not really add much value and do not highlight the important concepts
of classes, confusing the user and making things looks more complicated than they are
Fix yesterday's changes to currentGroupNode() (fixes addition of groups)
Remove some superfluous empty vertical space from browser dock widget
fix metasearch syntax error
fix metasearch typo (followup 5cb7d357)
german translation update