Allow to decode stack for binaries at any location

[Anton-V-K]

The tool works fine when decoding stack trace for ELF/HEX at the Arduino's build directory.
In some cases the binaries may be old (i.e. not freshly built), and they are located at other directory.

Use case:

1. Build a sketch and deploy it to a device.
2. Continue development (i.e. modify the code).
3. Receive crash report from a user for the deployed version.
4. Feed old HEX/ELF to the decoder along with the stack trace.

At the moment the step 4 should be preceded with extra actions: get corresponding sources from VCS and build them.

[me-no-dev]

I will take a look at how to trigger file open dialog, if that is possible :)

[me-no-dev]

FIXED! if elf is not found a dialog will be shown to manually locate it
please download latest release