swpagerelsize: add an eHeightPercentRelation member to SwFmtFrmSize

This is the doc model part, height.

Change-Id: I99eb4cadc2bd5f2025bc1b8793d4eede5b106d72
swpagerelsize: implement RelativeHeightRelation UNO property for SwXFrame

UNO API, height.

Change-Id: Ie61fb7f6de42b9dfb8b8f6f0982239d1c30f84ab
swpagerelsize: take care of GetHeightPercentRelation() in SwFlyFrm::CalcRel

Layout part, height.

Change-Id: Iee239e1a39dd495ee965ac45325a0f7087fdcdfa