Setting to turn of header cache

In application settings, there are now a, under cache tab a property to
turn off the header cache since it had been causing some trouble with
database locks.
Revert "Setting to turn of header cache"

This reverts commit e3befd4e433d87654cba76c6ad587c6bc5569133.
Settings to toggle header cache

Added a settings in application settings-> cache to turn off the header
cache
added french translation
removed dubble labels
Merge pull request #120 from ioVulture/master

Setting to enable or disable IfModified-headers/logic