lib/oe/package: add LOCALE_PATHS to add define all locations for locales

lib/oe/package: add LOCALE_PATHS to add define all locations for locales

Some packages may contain localized files not located in default path
${datadir}/locale. Add the new variable LOCALE_PATHS to allow a recipe
to define extra paths or even fully override the scanned directories.
LOCALE_PATHS is set at ${datadir}/locale by default to keep the exact
same behavior for the recipes which did not need modification.

Signed-off-by: Jonathan GUILLOT <jonathan@joggee.fr>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>