Browsertests: move creation of new properties to property_page

Follow-up to I3a55b3862f85bef7dbed9b5e133764b2b95d21db
Also moved the creation of new items to item_page.

Change-Id: I0e2c750e8deb5e7cc21f17db63422dea891f5b1a
Merge "Browsertests: move creation of new properties to property_page"