Log Message:
Update to 0.18:

Gaupol 0.18
===========

 * Add extension that allows use of custom framerates (#637503)
 * Add "Get more extensions" button to the preferences dialog
 * Relax SubRip file parsing in unambiguous cases (#634129)
 * Fix saving of last used directory in file dialogs with "paths that
   cannot be represented as a local filename" (#649347)
 * Add Brazilian Portuguese translation (Átila Camurça,
   Darlildo Souza)
 * Update German translation (Chris Leick)