Fix AppImage issues on linux

[ebma]

Adds an "afterPack" script for electron-builder that changes the permissions of the chrome-sandbox to 4755 to fix issues on some Linux distributions. This way users should not need to add the --no-sandbox attribute when running the .appimage.

I could not test it properly because I am not using a Debian based distribution.

Closes #1209.

[moranbw]

@ebma I tested this fix and I seem to get the following error:

The setuid sandbox is not running as root. Common causes:
  * An unprivileged process using ptrace on it, like a debugger.
  * A parent process set prctl(PR_SET_NO_NEW_PRIVS, ...)
Failed to move to new namespace: PID namespaces supported, Network namespace supported, but failed: errno = Operation not permitted
Trace/breakpoint trap

Do I need to clear any cache or anything like that?

• Debian 10 w/ MATE desktop

[andywer]

@ebma Can you please respond to @moranbw? Must have slipped through.

[andywer]

Nevermind. Just saw that the discussion was continued in the issue (#1209).

[andywer]

@ebma @moranbw Can we act on this PR or should we close it for now?

[ebma]

I guess we can close it for now. Although it fixes the original error about 'SUID sandbox helper binary was found, but is not configured correctly', it seems that there are more issues as @moranbw mentioned.

[andywer]

On hold.