re-implement most string methods, making TranslatableSetting an even better drop-in replacement

Signed-off-by: Chris “Kwpolska” Warrick <kwpolska@gmail.com>
add a __repr__ and a __dir__, refine some stuff

Signed-off-by: Chris “Kwpolska” Warrick <kwpolska@gmail.com>
return self from TS.__i*__() and TS.globformat()

Signed-off-by: Chris “Kwpolska” Warrick <kwpolska@gmail.com>
Merge pull request #1061 from getnikola/fix-multilang-settings

Fix TranslatableSetting by re-implementing string methods