Makes the tiles consistent as the participant view is equally sized and the
avatar is always centered in the tile.

Up until now we relied on implicit loading of middlewares and reducers, through
having imports in each feature's index.js.

This leads to many complex import cycles which result in (sometimes) hard to fix
bugs in addition to (often) breaking mobile because a web-only feature gets
imported on mobile too, thanks to the implicit loading.

This PR changes that to make the process explicit. Both middlewares and reducers
are imported in a single place, the app entrypoint. They have been divided into
3 categories: any, web and native, which represent each of the platforms
  respectively.

Ideally no feature should have an index.js exporting actions, action types and
components, but that's a larger ordeal, so this is just the first step in
getting there. In order to both set example and avoid large cycles the app
feature has been refactored to not have an idex.js itself.

* ref(display-name): do not pass in display name

The component gets the state itself from redux.

* fix(display-name): do not default name to placeholder name

The web display name component supports inline editing of
the name. Problems can occur when the displayed name
differs from the actual saved name, because participants
without a display name, including the local user, have
a different, default display name displayed. So when
editing starts, the input field is populated with the
default name. To workaround such while supporting fetching
the display name using mapStateToProps, pass in both the
name which should be shown and the name value saved in
settings.

* ref(display-name): rename methods

🔥🔥🔥

Co-authored-by: DimaG <dgeorgiev06@gmail.com>

For the most part the changes are taking the "static propTypes" declaration off
of components and declaring them as Flow types. Sometimes to support flow some
method signatures had to be added. There are some exceptions in which more had
to be done to tame the beast:
- AbstractVideoTrack: put in additional truthy checks for videoTrack.
- Video: add truthy checks for the _videoElement ref.
- shouldRenderVideoTrack function: Some component could pass null for the
  videoTrack argument and Flow wanted that called out explicitly.
- DisplayName: Add a truthy check for the input ref before acting on it.
- NumbersList: Move array checks inline for Flow to comprehend array methods
  could be called. Add type checks in the Object.entries loop as the value is
  assumed to be a mixed type by Flow.
- AbstractToolbarButton: add additional truthy check for passed in type.

* Removed unnecessary string wrapping

Prepare for React 16.

Create a new component that uses Dialog. Reuse existing actions
for updating a participant's display name.

* feat(display-name): convert to React

- Create a new React Component for displaying and updating display
  names on small videos
- The updating of the Component is defined in the parent class
  SmallVideo, which children will get access to through prototype
  copying
- Create a new actionType and middleware so name changes that occur
  in DisplayName can be propogated to outside redux
- Update the local video's DisplayName when a conference is joined
  or else the component may keep an undefined user id

* squash: query for the container, not the el owned by react