add vertical offset setting

[spongebyte]

Hi, it would be great to have a vertical offset setting.

Many thanks for this app.

[ykasidit]

Hello, this is now possible in settings or long click in map tab in latest version in google play, please try and let me know.

If you want to try the latest pre-release pls try below too: https://github.com/ykasidit/bluetooth_gnss/releases/tag/v3.0.1