Make search and settings pages adaptive in mobile-config-thunderbird

Thunderbird can be adapted to mobile using mobile-config-thunderbird (https://gitlab.postmarketos.org/postmarketOS/mobile-config-thunderbird) and it works really well (especially compared to mostly broken geary - also confirmed by many positive reviews by users. Additionally thunderbird has OpenPGP support which is missing in geary.) for reading and writing mails. But some parts like search and settings are not adaptive yet. I think having a good email app is important to daily driving a phone. So we should make the remaining screens adaptive as well.