[FL-2859,2838] fbt: improvements for FAPs (#1813)

* fbt: assets builder for apps WIP
* fbt: automatically building private fap assets
* docs: details on how to use image assets
* fbt: renamed fap_assets -> fap_icons
* fbt: support for fap_extbuild field
* docs: info on fap_extbuild
* fbt: added --proxy-env parame ter
* fbt: made firmware_cdb & updater_cdb targets always available
* fbt: renamed fap_icons -> fap_icon_assets
* fbt: deprecated firmware_* target names for faps; new alias is "fap_APPID"
* fbt: changed intermediate file locations for external apps
* fbt: support for fap_private_libs; docs: updates
* restored mbedtls as global lib
* scripts: lint.py: skip "lib" subfolder
* fbt: Sanity checks for building advanced faps as part of fw
* docs: info on fap_private_libs; fbt: optimized *.fam indexing
* fbt: cleanup; samples: added sample_icons app
* fbt: moved example app to applications/examples
* linter fix
* docs: readme fixes
* added applications/examples/application.fam stub
* docs: more info on private libs

Co-authored-by: あく <alleteam@gmail.com>

scripts/lint.py

@@ -54,6 +54,10 @@ class Main(App):
         output = []
         for folder in folders:
             for dirpath, dirnames, filenames in os.walk(folder):
+                # Skipping 3rd-party code - usually resides in subfolder "lib"
+                if "lib" in dirnames:
+                    dirnames.remove("lib")
+
                 for filename in filenames:
                     ext = os.path.splitext(filename.lower())[1]
                     if not ext in SOURCE_CODE_FILE_EXTENSIONS: