[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.

applications/cli/cli.c

@@ -51,7 +51,7 @@ size_t cli_read(Cli* cli, uint8_t* buffer, size_t size) {
 }
 
 bool cli_cmd_interrupt_received(Cli* cli) {
-    char c;
+    char c = '\0';
     api_hal_vcp_rx_with_timeout((uint8_t*)&c, 1, 1);
     return c == CliSymbolAsciiETX;
 }