Removes some messy code as a result of the old feature's removal.
Additionally, updated code style in ManagerCommands and fixed several nullable issues.
Implemented several workarounds to what appearto be a library bug in
which not all users will be downloaded onto the cache. User cache
checking and downloading is delegated to a new Common method and a
new BackgroundService, respectively.
This is hopefully temporary.
The BirthdayBot class has been split up into ShardInstance and
ShardManager. Several other things have been reorganized so that shards
may act independently.
The overall goal of these changes made is to limit failures to sections
that can easily be discarded and replaced.
All existing VB code was 'translated' to C# as closely as possible, with
minor changes and additional notes. Currently untested and likely
broken.
Further commits will go toward making overall improvements until this
version replaces the currently existing code.
