Excel as Term-Collection source

Extend the Term-Collection import with excel file as source.

Implementation tips:

Parse the excel file and generate tbx from it. Then use the current tbx parser to import the generated tbx into the term collection.

Add the excel file format to the TbxImport tests.

Filesystem and Across imports (documentation and config files to) should be able to handle the new excel file format.

For excel layout format ask marcmittag or aleksandar .