Add basic lazy gettext implementation

This is the first part of an implementation towards
a deferred localization functionality in OpenStack.
This change adds a Message class for encapsulating a
translatable message and its relevant data, as well
as an example LogHandler of how such a class can be
used in the logging context.

bp delayed-message-translation

Change-Id: I8485a346d32925327ea9185e0da3822e4e19c2f5
Merge "Add basic lazy gettext implementation"