Since 1d38cb36, "number format" and
"link number format to source" properties are 2 separate properties.  Adjust
OOXML import code for that split.

Also, always set axis' number format via NumberFormat property even when it's
a percent format.  The axis object doesn't keep a non-percent and percent
number formats separately.

Change-Id: I8667b6f1a78d88cc37d059518919ad1b37f154e1