remove unnecessary [GoBoardRegion hasPoint:]

this method is not necessary, instead one can compare the GoBoardRegion object
with the [GoPoint region] property; more importantly, the object comparison is more
efficient than the [GoBoardRegion hasPoint:] test, so much so that loading a large
game becomes significantly faster on older devices (cf. profiling information in issue
#113 for iPhone 3GS and the ear-reddening game).
add basic zooming
add double-tap zoom in, and two-finger-tap zoom out
cleanup PanGestureController
add logging to draw methods of PlayView layer delegates
fix/update various comments
add user preference "maximum zoom scale"
add profiling info regarding zooming to Research document
add moveNumber property to GoMove

this property is a pre-condition for feature "display move numbers"
add user preference "display move numbers"
draw move numbers
send archived games via email (closes #19)
add GoGameDocument to support concept of document dirty flag

this is a preparation step for the upcoming commits related to issues #42
("Display "discard old game" question only if game has not been saved")
and #20 ("Open .sgf files received via email").
bump NSCoding version number
"discard game in progress" question is now based on document dirty flag (closes #42)
fix NSCoding support in GoMove (move number was incorrectly stored as object)
use NSCoding to backup/restore the game in progress (closes #114)
disable resigning while viewing an old board position (fixes #115)
BackupGameCommand now saves an .sgf file only when explicitly requested

currently all actors that use BackupGameCommand *do* want to save an .sgf file,
but future actors sometimes will not want this
save application state more frequently (together with user preferences)

this change fully leverages the previous changes to BackupGameCommand and
RestoreGameCommand (both of which now work with an NSCoding archive);
because we now save application state on application suspend (and a few other
occasions), RestoreGameCommand is now capable of restoring not only the board
position, but also the GoGameDocument properties and the scoring mode state
(the latter has never been possible before).