MainFrm: Use GetFileName() when saving subtitles.

Fixes cases where URLs are being used as a suggested subtitle filename.
installer: Update Inno Setup's Basque translation.
PPageFileMediaInfo.cpp: Fix mismatching allocation and deallocation.

This was introduced in ecf6198ea30fb8888060360fa650b36c1c67cc69.
IsISO639Language: Fix a memory leak detected by Coverity.
Internal filters page: Add buttons to access filters properties.