Fix video play command in sample vifmrc file

Thanks to filterfalse.
Activate view-mode of preview on Ctrl-W movements
Extract switch_windows() func in modes/normal.c

To reduce code duplication.
Fix cursor position after view reload

Was broken while implementing stabilization of file under cursor on
resorting view.
Extract move_window() function in modes/normal.c

To reduce code duplication.
Move normal.c:switch_panes to ui.c

And rename it to switch_panes_content().
Move windows manip funcs from normal.c to ui.c
Make most of Ctrl-W x keys work in view mode
Change meaning of Ctrl-W H/J/K/L for preview
Fix Ctrl-W in preview/view mode
Add Ctrl-W o key to the view mode
Extract the view.c:display_error() function
Extract view.c:goto_search_result() function

To reduce code duplication.
Remove unused view.c:find_next() parameter
Rename parameter of view.c:find_previous()
Extract view.c:search() method

To reduce code duplication.
Add a workaround for "v" in view mode

In some cases two redraw operations are needed, otherwise TUI is
not fully redrawn.
Move commands.c:comm_only to ui.c:only
Update documentation on Ctrl-W x keys
Merge branch 'better-ctrl-w-in-view-mode'