Home: People invite UI fix

This branch fixes two issues:
It used to be that there were no limits on the number of people an user can invite. After this fix, the user be limited to inviting to up to 5 people. She/he will see the message "To keep the conversation close and meaningful, you can invite up to 5 people." displayed as the place holder text for the search box.
Question for @psybuzz, are users added based on the data-id that's in the DOM? I'm thinking of a senario when an user adds a person, but then removes the user from the selected list, is the person still added to the convo?

The second issue is that duplicate names are displayed when the user search for people. When a user selected a name, say 'Charles X', as one of the invitees, a subsequent search for 'Charles' will still show 'Charles X' in the dropdown of names. This push fixes that. Now the name is removed from the search results.
I think this comment has an extra space at the beginning (we need to delete one space before `//` to make it in line with the following code. We can also delete the extra line between this comment and the code that follows it to keep it consistent with other comments!

Also, for comments in general I think we're using the syntax of capitalizing the first letter and adding a period at the end. I'd change this comment to specify what the entire block of code below does, such as `// Check if any user included in the search results has already been selected for this conversation. If so, do not display this user's name in the search results.`