The whitelisting was hidden by the last release. You can whitelist by setting the desired blocking mode for the URL specifically. If you want to whitelist an URL just give it an "allow everything". You can still whitelist a site from the notifications. I should definitely clarify the description...

Adding an URL specific block mode:
go to options, click on the triangle next to the blocking mode, enter the domain you want to whitelist, click on the plus, now you can set the blocking mode for the domain.

PS: you can still enter something in the white list by checking expert mode, open the export settings page and entering something in the whitelist field.

EDIT: Is the screenshot of the settings not explanatory enough?
EDIT2: It's easier for us to communicate on github. If you have any questions - just open an issue. Here the communication is slow and not relyable.

EDIT3: please try version 0.4.4 - there the whitelist is available again.