wxGUI: icons for layers in lmgr tree without 'layer' and 'add' symbols

Size of icons is 16x16 to avoid imperfect resampling at some (or all) platforms.
The motivation is to make the icons more useful, they now can actually help to recognize type of layer.
The commit assumes that the icon objects defined in layertree are used only for layers, not for other things although item label suggests that.
Command and grid layer still use the layer-xxx-add icon because there is no SVG for them in OSGeo icons (trac.osgeo.org/osgeo/browser/graphics/trunk/).
Geodesic and rhumbline layers are already using an icon with this style (the same icon, actually).

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@61280 15284696-431f-4ddb-bdfa-cd5b030d7da7

gui/wxpython/lmgr/layertree.py

@@ -70,23 +70,23 @@ LMIcons = {
                             label = _('Add command layer')),
     'quit'       : MetaIcon(img = 'quit',
                             label = _('Quit')),
-    'layerRaster'    : MetaIcon(img = 'layer-raster-add',
+    'layerRaster'    : MetaIcon(img = 'raster',
                             label = _('Add raster map layer')),
-    'layerRgb'     : MetaIcon(img = 'layer-rgb-add',
+    'layerRgb'     : MetaIcon(img = 'rgb',
                             label = _('Add RGB map layer')),
-    'layerHis'     : MetaIcon(img = 'layer-his-add',
+    'layerHis'     : MetaIcon(img = 'his',
                                     label = _('Add HIS map layer')),
-    'layerShaded'  : MetaIcon(img = 'layer-shaded-relief-add',
+    'layerShaded'  : MetaIcon(img = 'shaded-relief',
                               label = _('Add shaded relief map layer')),
-    'layerRastarrow'  : MetaIcon(img = 'layer-aspect-arrow-add',
+    'layerRastarrow'  : MetaIcon(img = 'aspect-arrow',
                             label = _('Add raster flow arrows')),
-    'layerRastnum'    : MetaIcon(img = 'layer-cell-cats-add',
+    'layerRastnum'    : MetaIcon(img = 'cell-cats',
                             label = _('Add raster cell numbers')),
-    'layerVector'    : MetaIcon(img = 'layer-vector-add',
+    'layerVector'    : MetaIcon(img = 'vector',
                             label = _('Add vector map layer')),
-    'layerThememap': MetaIcon(img = 'layer-vector-thematic-add',
+    'layerThememap': MetaIcon(img = 'vector-thematic',
                             label = _('Add thematic area (choropleth) map layer')),
-    'layerThemechart'   : MetaIcon(img = 'layer-vector-chart-add',
+    'layerThemechart'   : MetaIcon(img = 'vector-chart',
                             label = _('Add thematic chart layer')),
     'layerGrid'    : MetaIcon(img = 'layer-grid-add',
                             label = _('Add grid layer')),
@@ -94,12 +94,12 @@ LMIcons = {
                             label = _('Add geodesic line layer')),
     'layerRhumb'   : MetaIcon(img = 'shortest-distance',
                             label = _('Add rhumbline layer')),
-    'layerLabels'  : MetaIcon(img = 'layer-label-add',
+    'layerLabels'  : MetaIcon(img = 'label',
                             label = _('Add labels')),
-    'layer3d-raster'  : MetaIcon(img = 'layer-raster3d-add',
+    'layer3d-raster'  : MetaIcon(img = 'raster3d',
                             label = _('Add 3D raster map layer'),
                             desc  =  _('Note that 3D raster data are rendered only in 3D view mode')),
-    'layerWms'      :  MetaIcon(img = 'layer-wms-add',
+    'layerWms'      :  MetaIcon(img = 'wms',
                             label = _('Add WMS layer.')),
     'layerOptions'  : MetaIcon(img = 'options',
                                label = _('Set options')),