src: main: importdata: Column: Cleanups and refinements
src: main: importdata: CSVConfiguration: Cleanups and refinements
src: main: importdata: DataSourceConfiguration: Cleanups and refinements
src: main: importdata: Refactor CSVConfiguration
src: main: importdata: Rename CSVConfiguration to CSVFileConfiguration
src: main: importdata: Rename FileConfiguration to DataSourceFileConfiguration
src: main: Move source configuration classes into io package

These classes could theoretically also be used to describe data sinks rather
than sources, so they are moved into a more generic package. Probably it would
also make sense to rename them, as "source" is technically not equal to "sink".
src: main: io: Rename header interface
src: main: io: importdata: DataSourceImportAdapter: Cleanups
src: main: io: importdata: CSVImportAdapter: Cleanups
src: main: importdata: Rename CSVImportAdapter to CSVFileImportAdapter
Merge branch 'master' into cleanup/importdata
Merge branch 'master' into cleanup/importdata
src: main: importdata: DataSourceImportAdapter: Change error message
src: main: importdata: Move fields into more generic class
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