catv: convert this bbox-specific applet into "cat -v"

catv: convert this bbox-specific applet into "cat -v"

function                                             old     new   delta
cat_main                                             150     320    +170
packed_usage                                       31511   31552     +41
applet_install_loc                                   190     189      -1
applet_main                                         1516    1512      -4
applet_names                                        2618    2613      -5
catv_main                                            227       -    -227
------------------------------------------------------------------------------
(add/remove: 0/2 grow/shrink: 2/3 up/down: 211/-237)          Total: -26 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>