The image pickers read the camera folder

The attach picker only looked in the app's own folder. The console's camera saves photos as DCIM/<folder>/<image>, so the picker now lists those too.

Changes

• Wolfram wf_attach_scan_images_tree (#194, released in v0.39.0 via #195). It lists a folder's images and those one folder down, with entries as folder/name. Two levels down is not read.
• Indigo (#74): the app folder first, then sdmc:/DCIM. Camera rows are labelled and open from their own path. The list holds 23 rows across both folders.
• Cobalt (#206): the app folder first, then sd:/DCIM (the Wii U's equivalent), capped at 64 rows.

Limits

• Cobalt's app images come first, so with 64 or more of them the camera folder shows nothing.
• Indigo takes the first camera matches in directory order, not the newest.

Verification

• Wolfram: 27 attach checks.
• Indigo: 4065 host checks, and the 3DS cross-build links.
• Cobalt: 1036 host checks, sweep and linkcheck.
• Azahar: Indigo's picker was checked on the emulator's own folder only. The DCIM listing has not been seen on a 3DS or in Azahar, and nothing has been run on a Wii U.