Add panes splitting, auto filter and selection features.

[GMolini]

This pull request has features copied from @agrech , which proposed them for the original repository of @dbzhang800

I have merely copied his code and would like to include them in this version.

Add worksheet pane splitting features with methods:

• freezePane() : Create panes and mark them as frozen in worksheet's spreadsheetML.
• splitPane(): Create panes and mark them as split in worksheet's spreadsheetML. Auto filter feature:
• setAutoFilter(): Mark a range of cells for auto filtering. Selection feature:
• setSelection(): Select a cell range and activate a cell for a pane in a worksheet.

Existing panes, auto filter and selections will also be imported on opening an existing xlsx file.