v2 - provide AutoUpdate for desktop installer

[jgadsden]

This issue has been migrated from: https://github.com/mike-goodwin/owasp-threat-dragon-desktop/issues/101

There is a branch for applying auto-updates using squirrel. It should be cross platform for Windows, MacOS and Linux. File app/app.js has been modified to not use autoupdate via PR OWASP/threat-dragon-desktop#102 because it was causing problems, but this modification can be undone when autoupdate is working:

//electron autoupdate
//Note: autoupdate has been disabled until this issue has been satisfied:
//      https://github.com/mike-goodwin/owasp-threat-dragon-desktop/issues/101
// app.run(['common', 'dialogs', 'electron', 'VERSION', require('./app/config.autoupdate')]);

[jgadsden]

Use update-electron-app: https://www.electronjs.org/docs/tutorial/updates

[jgadsden]

Auto update requires a signed application, which is proving a problem - see OWASP/threat-dragon#219 "TDD 1.3 not a trusted app for both Windows and Apple" raised by @lmcthbe

[jgadsden]

Transferred to threat dragon repo

[lreading]

This can probably be looked into again, as MacOS signing is done and Windows signing will be done in the very near future.

[jgadsden]

With both MacOS and Windows signing in place, this can be considered for version 2.0. It is not a pre-requisite for the version 2.0 release, but it would be nice to have. It depends on having the electron wrapper in place, subject of #334 "Version 2.0: desktop version"

[jgadsden]

It may be easiest to use electron's auto-updater: https://www.electronjs.org/docs/latest/tutorial/updates

[jgadsden]

Decided to use electron/update-electron-app