Merge pull request #1390 from Cracert/i18n

[TRANSUP] pl: MetaSearch
restore previous Qgs(App)LegendInterface behaviour
[Plugin Manager] Show all plugins in the All tab. Fixes #10334
[processing] fixed #10364
[layertree] do not allow drag'n'drop of internal embedded nodes
[layertree] Fix #10347 - save also old <legend> tag

QGIS server does not use QgsProject for loading of QGIS project.
In order to allow reading of new projects, let's also write the original <legend> tag to the project.
Ideally the server should be ported to new layer tree implementation, but that requires
non-trivial changes to the server components.
The <legend> tag is ignored by QGIS application in >= 2.4 and this way also the new project files
can be opened in older versions of QGIS without loosing information about layer groups.
[layertree] Add docs to QgsLayerTreeUtils
Attribute table: Fix repaint on change
Fix #10345
Fix #10366 (geometry functions not working in rule test)
[layertree] Added QgsLayerTreeModel doxygen docs + minor API changes
[layertree] Fix #10373 (embedded group not loaded if with relative path)
[layertree] Use writePath() for embedded groups (absolute vs relative path)
[TRANSUP] pl: SelectionPanel, QObject, App, LayerTreeView