recent-view: Verify a path exists before adding an icon

Fixes warnings when switching from the recent view to
a document back and forth.
shell: Make a class for EvToolbar to abstract for other toolbars
ev-recent-view-toolbar: Implement a different toolbar for recent view

Added a new EvRecentViewToolbar which is displayed while in
recent view, instead of the full regular toolbar.
ev-toolbar-main: Add recent view show toolbar button
ev-window: Integrate the recent view
ev-window: Removed the recent menu list

Since we have EvRecentView now, there is no use of the menu of recent items.
Removing it.