[Shotwell] Adding simplified Chinese translation

[Lucas Beeler]

Hi Tommy,

   The Transifex online translation system appears to have problems
working with PO files having more than 100 strings. The web-based
editing component of Transifex is called Lotte. Up until release 0.7
of Transifex, Lotte was limited solely to 100 string or less PO files
(see http://docs.transifex.org/releases/0.7.html for details). In the
current release of Transifex server (0.8) the previous hard 100 string
restriction was removed. However, we still get anecdotal reports of
Lotte having trouble with large PO files (your report being yet
another example). Since the Shotwell POT file has over 400
translatable strings, we definitely don't recommend using Lotte to
edit it online. Instead, we recommend using POEdit or a similar
desktop translation app. Once again, this is an ongoing limitation of
the Transifex server software and we apologize for the inconvenience.

Take care,
Lucas