Allow translations of the effects files

The effect files are not translatable at the moment. The issue lies in the fact that, even though the effect uses the Desktop entry specification, it is not recongnized as such by gettext because it uses the file extension to detect the supported files.

As a workaround for this problem, the files has been renamed to include the desktop extension, which helps gettext detecting the effect files. After the translation merge process they are renamed to their right name without the desktop extension.

Refs !1 (merged)