Rework the depot browser layout and confirm a crewless start

The vehicle database panel loses its header bar and packs the search box and
the archival filter into one line, the class combo takes a full-width line of
its own with a miniature (big in the drop-down, one line when closed) and the
bulk / texture-base actions move into the Add button's drop-down. The mini
preview sits beside the texture data and stays hidden until an entry is
picked, so the list keeps the space.

Picking a class or a vehicle now fills both combos in, and a class alone is a
valid filter (it used to leave the list empty without a category). The combos
and the list are rebuilt on the next dispatcher pass, since clearing Items
from inside the SelectionChanged that asked for it throws.

Vehicle removal becomes a per-card tool next to flip / crew, the scenery and
vehicle names move into their panel headers, and the texture randomizer
dialog sizes to its content instead of clipping its last button.

Start no longer hides behind Ctrl: a consist with no crew and no passenger
says so on the button and asks for confirmation before launching.

StarterNG/startercfg/lang/cz.xml

@@ -56,7 +56,9 @@
     <String key="Start">Spustit</String>
     <String key="StartNoScenery">Select a scenery</String>
     <String key="StartNoTrain">Select a consist</String>
-    <String key="StartNoStaff">No crew / passenger (hold Ctrl to start)</String>
+    <String key="StartNoStaff">No crew / passenger</String>
+    <String key="StartNoStaffTitle">Consist without crew</String>
+    <String key="StartNoStaffConfirm">This consist has no crew and no passenger — there will be nothing to drive. Start anyway?</String>
     <String key="RestoreWeather">Restore weather</String>
     <String key="ReloadSceneries">Reload</String>
     <String key="OpenSceneryFolder">Open folder</String>