#103 make submit buttons more translation/modification friendly

[Oliver M. Bolzer]

Attached is patch that allows more freedom in changing
the value of various submit buttons, so that the
op-table doesn't need to be updated each time the
button label is changed.

This is done by decoding form parameters that are named
op_foo into op=foo.

Further description in
https://sourceforge.net/mailarchive/forum.php?thread_id=3870371&forum_id=4018

[Oliver M. Bolzer]

decode op_foo into op=foo