[FL-1443, FL-1289] Move assets compilation to separate Makefile. Add scripts folder. Add OTP flashing with DFU. (#531)

* Assets: move assets compilation to separate Makefile. Move all scripts to scripts folder. Add scripts ReadMe. Add precompiled assets.
* Split assets.py into separate entities. Option bytes for FL-1289 and checker/setter.
* Cli: explicitly initialize variable befor use in api_hal_vcp_rx_with_timeout
* Rename ob_check script to ob.

scripts/ReadMe.md

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+# About
+
+This folder contains differnt scripts that automates routine actions.
+Flashing scripts are based on cli version of [STM32CubeProgrammer](https://www.st.com/en/development-tools/stm32cubeprog.html).
+You will need to add STM32_Programmer_CLI to your path to use them.
+
+# Flashing empty MCU/Flipper
+
+Always flash your device in the folllowing sequence:
+
+- OTP (Only on empty MCU)
+- Core2 firmware
+- Core1 firmware
+- Option Bytes
+
+## Otp flashing
+
+!!! Flashing incorrect OTP may permanently brick your device !!!
+
+Normally OTP data generated and flashed at factory.
+In case if MCU was replaced you'll need correct OTP data to be able to use companion applications.
+Use `otp.py` to generate OTP data and `flash_otp_version_*` to flash OTP zone.
+You will need exact main board revision to genrate OTP data. It can be found on main PCB.
+
+!!! Flashing incorrect OTP may permanently brick your device !!!
+
+## Core2 flashing
+
+Script blindly updates FUS and Radiostack. This operation is going to corrupt bootloader and firmware.
+Reflash Core1 after Core2.
+
+## Core1 flashing
+
+Script compiles and flashes both bootloader and firmware.
+
+## Option Bytes
+
+!!! Setting incorrect Otion Bytes may brick your MCU !!!
+
+Defaults are mostly OK, but there are couple things that we'd like to tune.
+Also OB may be damaged, so we've made couple scripts to check and set option bytes.
+
+!!! Setting incorrect Otion Bytes may brick your MCU !!!
+
+Checking option bytes:
+
+	ob.py check
+
+Setting option bytes:
+
+	ob.py set