[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.

assets/ReadMe.md

@@ -1,3 +1,13 @@
+# Requirements
+
+- Python3
+- ImageMagic
+- Make
+
+# Compiling
+
+	make all
+
 # Asset naming rules
 
 ## Images and Animations