Release pushed ATN

3.0.0beta3

set two line header mode for test of header button icon/label

Release pushed ATN

3.0.0beta2

Disable another test for beta+

Version uploaded to ATN

Version bump for upload at ANN:

https://developer.thunderbird.net/add-ons/tb68#uploading-your-updated-add-on

First beta for Thunderbird 68.0

2.3.0beta1

Again use force-local argument in tar command.