Protect or unprotect worksheets in Excel file

Protect or unprotect selected worksheets in Excel file, with or without password

USAGE
xls_protect_sheets(xlsfile,sheets,action)
xls_protect_sheets(xlsfile,sheets,action,password)

INPUT
- XLSFILE: name of the Excel file
- SHEETS: cell array with the worksheet names, or matrix with positive integers, or 'all', to tell which worksheets are going to be protected
- ACTION: 'protect' or 'unprotect'
- PASSWORD: password to protect or unprotect the worksheet

OUTPUT
- XLSFILE will be edited