Add generic CSV export translator
* BOM on export, which is required for Excel not to mess up charset when opening the file, depends on zotero/zotero#517
* To avoid Excel from interpreting some fields as dates (e.g. some page ranges), it's best to import the CSV file into Excel as text data with commas as field delimiters and marking all columns explicitly as text. This messes up UTF-8 encoding though.

Thanks to @zuphilip for the initial code
Closes #742

Signed-off-by: @aurimasv