data: Add test.xls

The content was taken from test.csv. It will be used for examples of the XLS
import API.
data: Add test.xlsx

The content was taken from test.xls. It will be used for examples of the XLSX
import API.
lib: Add poi-ooxml for XLSX files
src: main: importdata: Add setContainsHeader() to interface
lib: poi: Add complete package
src: main: importdata: Add Excel import functionality
src: main: importdata: ExcelFileImportAdapter: Implement getProgress()
src: gui: wizard: importdata: Rename XLS page to Excel page
src: gui: wizard: importdata: Enable Excel page
src: gui: wizard: importdata: Rename button
src: gui: wizard: importdata: Rename SourceType.XLS to SourceType.EXCEL
src: gui: wizard: importdata: Rename xlsSheetIndex to excelSheetIndex
src: main: importdata: DataSourceConfiguration: addColumn(): No exception
src: gui: wizard: importdata: SourcePage: Swap Excel and JDBC
src: gui: wizard: importdata: Implement ExcelPage
src: gui: wizard: importdata: CsvPage: Fix bug when selecting multiple times
src: gui: wizard: importdata: CsvPage: Simplify event listening
src: gui: wizard: importdata: CsvPage: Make some widgets invisible in the beginning
src: gui: wizard: importdata: CsvPage: Cleanups and refinements
Add copyright notices with proper authors