Manual: Be more accurate about 'reset settings with button during startup' - the...

Manual: Be more accurate about 'reset settings with button during startup' - the feature wasn't mentioned in some manuals even though it is possible (Sansas, Iaudios, H10s); use the *_PAD macros because it depends on the keypad and this way it's easier to exclude it from the 1st-3rd gen Ipod manuals (currently not possible on these targets); use the 'press button' phrasing for the Gigabeat (still not perfect but better than before).

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@16119 a1c6a512-1295-4272-9138-f99709370657