Add parsting `sheets` elements of `workbook.xml`

[ShockwaveNN]

Workbook usually looks like this

<workbook xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main" xmlns:r="http://schemas.openxmlformats.org/officeDocument/2006/relationships">
  <workbookPr/>
  <bookViews>
    <workbookView xWindow="360" yWindow="15" windowWidth="20955" windowHeight="9720" activeTab="1"/>
  </bookViews>
  <sheets>
    <sheet name="Sheet1" sheetId="1" state="hidden" r:id="rId1"/>
    <sheet name="new_sheet" sheetId="2" state="visible" r:id="rId2"/>
  </sheets>
  <calcPr/>
</workbook>

Seems that we're parsing some sheet data in those lines
But I think we need to add parsing of sheets as a whole

For example seems that now we cannot parse state at all