Read CSV format filter files

[AdamCarroll]

VocabHunter allows users to filter out lists of words that they already know. These lists can come in the form of text documents (read using Apache Tika) or Excel spreadsheets with one or more columns of words (read using Apache POI). It should also be possible to read CSV format filter files.

Ideally this should be implemented using a standard Open Source CSV reader component. The key interface for this work is TextGrid.

See also: #21