Add a delay to loading peeked conversations

Don't instantly start loading a peeked conversation
when the user is navigating with the keyboard.
This prevents the app from freaking out when the
user is trying to quickly scroll down the TL.

Current delay is 500ms.

b/3304236

Change-Id: I5bbdafc5187a7f2b96e28aed1b60b694d4565db1
2 files changed