Internationalized fields initialised with empty strings remain empty.

In the factory classes when an internationalized field such as the
description or comment fields on Entry are initialized the value
was prefixed with the name of the language so it was easy to spot if
there were any bugs in selecting the correct translation. The language
prefix was added even if the string was blank. This caused a problem
on creating fixtures for Entry objects where the description field, if
set, was displayed in preference to the basic count. The _i18n_kwrags
method in the LanguageFieldMixin was updated so the prefix is only
added if the value used to initialize a field is not an empty string.
Updted version number for release
Merge branch 'release-0.4.1' into develop