* fbt: replaced debug dir paths with FBT_DEBUG_DIR
* scripts: updated requirements.txt
* fbt: fixed wrong import
* fbt: removed delayed import for file2image
* fbt: added UPDATE_BUNDLE_DIR internal var
* fbt: cleaner internal management of extapps
* applications: added fap_libs for core apps to link with resources when building with --extra-ext-apps
* fbt: removed deprecation stub for faps
* fbt: added quotation for icons build cmd
* fbt: reworked BUILD_DIR & fap work dir handling; fap debug: using debug elf path from fbt
* fbt: explicit LIB_DIST_DIR
