added mode to patch tapes to force visible playfield size of 34 x 34

This adds a new tape patch mode "screen_34x34" that can be used to
patch existing tapes to force a visible playfield size of 34 x 34
tiles (as used with setup option "small game graphics" when using a
graphics set with classic visible playfield size of 17 x 17 tiles).

This patch mode can be applied to team mode tapes only.

This patch mode can be used to fix broken tapes caused by recording
tapes in team mode and then replaying them with a different visible
playfield size, potentially causing different player movement due to
players being unable to move when reaching the edge of the visible
playfield when another player stays at the opposite screen border,
with default player focus that forces all players to be inside the
visible playfield.