Improve discusion refresh perf in DiscussionStore and messageStore

[fleandrei]

In DiscussionStore.tsx,

gossip/src/stores/discussionStore.tsx

Lines 193 to 200 in 0e3708a

	sdk.on(SdkEventType.MESSAGE_RECEIVED, onEvent);
	sdk.on(SdkEventType.MESSAGE_READ, onEvent);
	sdk.on(SdkEventType.SESSION_CREATED, onEvent);
	sdk.on(SdkEventType.SESSION_ACCEPTED, onEvent);
	sdk.on(SdkEventType.SESSION_RENEWED, onEvent);
	sdk.on(SdkEventType.SESSION_REQUESTED, onEvent);
	sdk.on(SdkEventType.DISCUSSION_UPDATED, onEvent);

we reload all discussions. It would be better to filter pertinent events and reload from db only data that is required. For exammple when a message is received, we can just refetch the discussion corresponding to this message rather than all discusions.
Same logic for messageStore.tsx