fix reading even/odd page breaks from .docx (bnc#519228)

We map Word's even/odd page breaks to Writer's left/right page styles. And we cannot
just set any page style to be left/right, because that could set e.g. the default
page style as such, which would make all normal pages that way. So instead we need
to make a copy of the relevant page style, as the original page style as its follow,
copy all the properties and headers/footers, and use this copy to get the page break.

Change-Id: Id0d2568de91ac2de4afb0ba3a6eedd9cec46f878