Implement private read receipts and typing indicators

[Grafcube]

Includes options for room specific overrides. The benefit of this implementation is that you can have different preferences for different accounts and those settings are restored on new devices.

I am very inexperienced with Flutter so there may be mistakes.

Fixes #456
Fixes #645

Screenshots

Global preferences:

Room overrides:

[Airyzz]

Thanks for this! Looks like a great addition, but needs some changes in how its implemented.

The biggest issue to me is that there is a lot of repeated code around getting and parsing settings from account data. Instead, I'd suggest adding the following to ReadReceiptComponent and TypingIndicatorComponent

// ReadReceiptComponent
bool get usePublicReadReceipts;
bool usePublicReadReceiptsForRoom(Room room);
Future<void> setUsePublicReadReceipts(bool value);
Future<void> setUsePublicReadReceiptsForRoom(Room room, bool value);

// TypingIndicatorComponent
bool get typingIndicatorsEnabled;
bool typingIndicatorsEnabledForRoom(Room room);
Future<void> setTypingIndicatorsEnabled(bool value);
Future<void> setTypingIndicatorsEnabledForRoom(Room room, bool value);

And then just accessing these throughout the app instead.

Let me know if you have any questions!

[Grafcube]

I have made all the requested changes

[Airyzz]

Thank you, looks much better now! I made a few small tweaks, mostly just UI things and changing the wording on some text. Let me know if you have any problem with those changes, otherwise I think this is good to merge

[Grafcube]

Looks good 👍 I also think it's good to go now.