Warn user of naming collisions when renaming or saving an object

[cjcenizal]

@LeeDr mentioned how confusing it is to have saved objects with the same names, and how easy it is to accidentally do so.

When saving an object or renaming it, we could present a typeahead that shows the user a list of similarly-named objects. This gives the user context when choosing a name, and allows him/her to avoid collisions.

[stacey-gammon]

How do we want to handle case in this situation? Should "New Visualization" give a warning if there is a an object with title "new visualization"? I'm thinking no... case sensitive, exact match.

[cjcenizal]

Since this is a UX issue, I think we should solve this from the user's perspective. As a user, I don't think I'm going to remember if (or even know why) an object is named with a particular capitalization scheme. So, to me, I would want to know that "Awesome Dashboard" already exists if I'm trying to name something "Awesome dashboard". So let's make it case-insensitive.