I decided to create my own and not to use a community package, because
1. it's straightforward
2. it's better integrated with our others libs such as EscapeActions
3. monitoring third-party packages evolutions (eg, CSS changes) is a
lot of work.
This is basically the same rationale than for our other generic UI
components such as the Popup/Popover.
This commit also slightly modify the general layout to remove
unnecessary wrapper DOM nodes.
Motivations:
* Iron-Router foces us to use Tracker.nonreactive black magic in order
to avoid un-necessary re-renders;
* There is a community consensus (supported by some MDG members) that
the flow-router API is easier to reason about;
* The useraccounts now supports flow router (that was a blocking
element when I considered the switch ~3months ago)
On the server we use the Picker router, as encouraged by the Kadira
team (which develop both Flow and Picker routers).
In the current state of things there are some bugs related to the
missing Loading architecure. Previously onRendered callback where
always called when the data the component needed was available, now
we have to handle this ourselves, which we will in a following commit.
