Change finding out whether the application is a portable instance

This fixes issue #58

If the application doesn't run from a usual installation path, it is
assumed that it is a portable instance. No extra steps during the
installation process needed!

Following environment variables are used:
- ProgramFiles: usual global path for 64 bits applications
- LOCALAPPDATA: usual user local path for applications

Update Electron

For Playwright is also an update available but it doesn't run with the
current Electron.

See issue Playwright issue #30755
microsoft/playwright#30755

Update dependencies, bump version to 3.1.0

Take care that header IDs are not confused with layout element IDs

This fixes issue #47

For the most part, it was a problem with not strict enough CSS
selectors.

Refactoring

Minor optimization at package size

Ignore additional files in electron-builder

Update dependencies

Update dependencies

Fix about dialog

Changed path to application icon had to be updated.