[Snails] Added folder to MailModel.
[Snails] Added default values to MailModel.
[Snails] Proper MailModel::data() function.
[Snails] MailModel::{Clear,Append}().
[Snails] MailModel::Update().
[Snails] Migrate to MailModel everywhere.
[Snails] Get rid of MailModelManager.
[Snails] Proper MailModel::headerData().
[Syncer] Fixed a copypaste error.
[Snails] More up-to-date CMakeLists.txt header.
[Snails] Message can have no From header.
[Snails] Chunked messages fetching.
[Snails] Style fixes.