filter trade stats by date range
Adds constraints to distribution_references table, as well as an unique index on distribution_id and reference_id
Only set updated_at and created_at for distribution_references where these are NULL
removing some strange characters, which appeared due to copy paste
Update updated_at if null, and created_at if null
Merge branch 'distribution_references_timestamps' into develop
added filter by purpose T and simplified constructor params
make travis happy
[#64037166] changed column label
bumped version to 0.6.0
remove \n\r chars from footnotes (only \newline is allowed for line breaks)
Revert "fixed pdflatex problem (newlines in footnotes)"

This reverts commit 0ffe71e424cc5ff3f0b4d47687cfb563426115e4.
formatting info
Merge branch 'hotfix-0.5.2' into develop