[css-page] Editorial issues regarding @page descriptors

The @page rule defines several descriptors ('size', 'marks', 'bleed', maybe
others I missed), which are called 'property' throughout the text. These
should be renamed to 'descriptor' for clarification and consistency.

Also, at the descriptor table[1] there is currently only 'bleed' listed.

Sebastian

[1] http://dev.w3.org/csswg/css-page-3/#page-descriptor-table