Images linting: ensure that all images conform specification

[skyhawkillusions]

What's new

• Since there was substantial inconsistency in the background design of the icon assets, I took the effort to standardize all of these. Any icons with transparent/orange BG has been converted to pure monochrome black/white
• fbt: added lint_img, format_img targets for processing images
• fbt: also added lint_all and format_all targets, invoking all linters and formatters
• github: now checking image formatting in linter workflow

Verification

• Upon sideloading these icons, check any and all applications that utilize the changed icons.
• Check new targets, try adding images straight from image editors and run fbt lint_img

Checklist (For Reviewer)

• PR has description of feature/bug or link to Confluence/Jira task
• Description contains actions to verify feature/bugfix
• I've built this code, uploaded it to the device and verified feature/bugfix

[hedger]

I went on and re-processed all .png files in assets and applications folders with

for f in `find assets applications -iname "*.png"`; do echo $f; magick $f -alpha off +profile "*" -define png:exclude-chunks=date,time -threshold "50%" -colors 2 $f.o && mv $f.o $f; done

or

find assets applications -iname "*.png" | xargs -P `getconf _NPROCESSORS_ONLN` -I F -n 1 sh -c 'mogrify -alpha off +profile "*" -define png:exclude-chunks=date,time -threshold "50%" -colors 2 F'