Feature: Highlight conflicting Talks!

[ShamiTomita]

Feedback: I noticed that I can add conflicting talks to my schedule. It would be nice if the app warned me that I had conflicting talk. Here are two possible ways this could be done: 1) notification at point of adding that there is a time conflict with another talk, 2) highlight the conflicting talks in My Schedule.

We should create a way to show the user that they have talks whose times conflict with each other.