Images linting: ensure that all images conform specification (#3802)

* Change all icons to be white background
* assets: re-processed all *.png images to 1-bit
* assets: also stripped profile data from .pngs
* assets: also stripped datetime from metadata (`-define png:exclude-chunks=date,time`)
* scripts: added image linter and formatter; fbt: added `lint_img` && `format_img` targets; github: integrated image lint step into CI
* scripts: imglint: fixed deprecation warning
* images: applied `format_img`
* fbt: added `lint_all` and `format_all` targets; docs: updated for new targets

Co-authored-by: hedger <hedger@nanode.su>
Co-authored-by: hedger <hedger@users.noreply.github.com>

documentation/fbt.md

@@ -78,6 +78,8 @@ To use language servers other than the default VS Code C/C++ language server, us
 - `get_stlink` - output serial numbers for attached STLink probes. Used for specifying an adapter with `SWD_TRANSPORT_SERIAL=...`.
 - `lint`, `format` - run clang-format on the C source code to check and reformat it according to the `.clang-format` specs. Supports `ARGS="..."` to pass extra arguments to clang-format.
 - `lint_py`, `format_py` - run [black](https://black.readthedocs.io/en/stable/index.html) on the Python source code, build system files & application manifests. Supports `ARGS="..."` to pass extra arguments to black.
+- `lint_img`, `format_img` - check the image assets for errors and format them. Enforces color depth and strips metadata.
+- `lint_all`, `format_all` - run all linters and formatters.
 - `firmware_pvs` - generate a PVS Studio report for the firmware. Requires PVS Studio to be available on your system's `PATH`.
 - `doxygen` - generate Doxygen documentation for the firmware. `doxy` target also opens web browser to view the generated documentation.
 - `cli` - start a Flipper CLI session over USB.