feat: Initial support for filtering notifications by sending account

[nikclayton]

Allow the user to define filtering rules for notifications by sending account:

• Not followed
• Younger than 30d
• Limited by moderators

and a policy for each of either show, warn, or hide.

To do this:

Manage followers

• Create a new FollowingAccountEntity, to record accounts the logged in account is following.
• Fetch the account's followers when an account is made active, and persist to this table.
• Provide the followers as a property on PachliAccount
• Update this table if the user follows/unfollows accounts during normal operation.

Track account creation time

• Record account creation time in TimelineAccount.

Track notification creation time

• Record notification creation time in Notification.

API

• Always fetch all notifications, including those the server is filtering.

UX and storage for account filters

• Show a new Account preference to edit account notification filters.
• Display a dialog to manage account notification filters.
• Persist the user's choice to new properties in AccountEntity.
• New AccountManager methods to update the properties

Filtering notifications

• New NotificationFilter.filterNotificationByAccount() method to make the filtering decision based on the user's preferences.
• Use this in NotificationFetcher to filter notifications before creating Android notifications.
• Use this in NotificationsViewModel to filter notifications before display in NotificationsFragment.

UX for filtered notifications

• Display filtered (with warning) notifications inline with other notifications, with UI to disclose the notification or edit the filters.