Fix issue #138 : not truly 1 second clip

[clinden]

This PR addresses issue #138 by implementing the author's proposed solution from discussion #119

• Added an option in the preferences page to pad short clips (< 1500 ms) with an additional 500 ms (default: disabled, so no extra milliseconds are added).
• Modified the video editor to pad clips with 500 ms if the option is enabled in preferences and the clip duration is less than 1500 ms.
• Added translations for multiple languages.

Note :
Most translations were generated using Google Translate and may not be entirely accurate, except for French which has been verified, and English which should be acceptable but might still need a review.