Remove hex manipulation code and use Nordic Intel Hex lib

[microbit-carlos]

Uses https://github.com/NordicSemiconductor/nrf-intel-hex, included as static/js/intel-hex.browser.js.

@microbit-rosslowe Can you review?

[microbit-rosslowe]

Odd bug in Safari Version 12.0.1 (14606.2.104.1.1), using a micro:bit 1.3b:

DAPLink Firmware - see https://mbed.com/daplink
Version: 0234
Build:   Oct 12 2015 14:53:22

I tested the basic, initial hello world script. In this PR, I get this hex file:
Unknown.zip

When attempting to flash the process appears to time out, and when the micro:bit is ejected it needs to be disconnected and reconnected.

The file works on my 1.5 if you rename to .hex:

# DAPLink Firmware - see https://mbed.com/daplink
Unique ID: 9901000050244e45003a2009000000670000000097969901
HIC ID: 97969901
Auto Reset: 1
Automation allowed: 0
Overflow detection: 0
Daplink Mode: Interface
Interface Version: 0249
Bootloader Version: 0243
Git SHA: 9c5fd81e6545d00b7f7c21ca9d8577dbd6a5fed2
Local Mods: 0
USB Interfaces: MSD, CDC, HID, WebUSB
Bootloader CRC: 0x32eb3cfd
Interface CRC: 0xcdb7b2a3
Remount count: 1
URL: https://microbit.org/device/?id=9901&v=0249

The first time I didn't rename I got a FAIL.TXT, which mentioned something about a time out. But since trying again this flashed fine.

[microbit-rosslowe]

Chrome downloads this as .hex, as expected, but this file still won't flash properly to the 1.3. On master, this produces a file that flashes fine.

https://python.microbit.org/v/0 works fine, and will flash without renaming to .hex.
Tested this on another 1.3, same version of DAPLink; same outcome.

[microbit-carlos]

@microbit-rosslowe I've updated the code to pad the code so that it works in older versions of DAPLink, could you test again?
(Safari should still have the "unknown" filename issue, but adding the .hex extension should work).

[microbit-rosslowe]

Thanks @microbit-carlos this works on both versions of DAPLink now.