fix #986 — strip leading slashes from joined URLs to make nikola-in-a-subdirectory work

Signed-off-by: Chris “Kwpolska” Warrick <kwpolska@gmail.com>
fix the urljoins -- was crashing due to an Undefined object

Signed-off-by: Chris “Kwpolska” Warrick <kwpolska@gmail.com>
add new translations to changelog

Signed-off-by: Chris “Kwpolska” Warrick <kwpolska@gmail.com>