Adds photo support

[agsalguero]

Description

Create videos from photos.

Checklist

• I have added a description of the change in CHANGELOG.md.
• I have added my name in the CONTRIBUTORS.md file, if it wasn't already present.

[KyleKun]

Hey @agsalguero, thanks so much for the contributions! I'll try to review all until this weekend, I just want to ask 2 points beforehand:

• Can you make the .5 trimmer values optional? A switch inside preferences, so we only show it when enabled.

• Does photos work in vertical mode too? (There's an open PR for this).

[agsalguero]

I have added an option in preferences to enable the "extended" version of quickcut buttons for both photos and videos. The default list is now [1, 2, 3, 5, 10] while the extended version is [1, 1.5, 2, 3, 4, 5, 6, 7, 8, 9, 10]. Change those values as you want but please keep 1.5 value, as it is the duration of favourite videos in the app (most of) us came from ;-).

IMPORTANT: in order for this PR to work you will also need to accept the PR for the video_trimmer subproject (KyleKun/video_trimmer#1) I send some days ago, since the list of quickcut durations is now passed as an optional parameter.

Edit: I've not tested the vertical mode but there might be some conflicts since the ffmpeg command is also altered. I'll review the code once the other PR is accepted.