added support for non preffixed page-spread-.. propertiesadded support for non preffixed page-spread-.. properties
Merge branch 'develop' into feature/support_non_prefixed_page_spread_property

Conflicts:
	ePub3/ePub/property.cpp
Merge pull request #104 from readium/feature/support_non_prefixed_page_spread_property

Support for non-prefixed "page spread" property