Upgrade core to 0.7.0
Background
In order to support attaching metadata feature, we need to update to the version of core which has it - 0.7.0 when after it's released. This task should be the prerequisite for this issue: https://gitlab.com/eyeo/adblockplus/abc/webext-sdk/-/issues/157
What to change
Upgrade core to 0.7.0. Implement all necessary changes if needed.