This allows to reduce the loading time of a big board.
Note that there is an infinite scroll implementation in the mixins,
but this doesn't fit well as the cards in the list can have arbitrary
height.
The idea to rely on the visibility of a spinner is based on
http://www.meteorpedia.com/read/Infinite_Scrolling
This commit stands on the initial support implemented in #342. We now
avoid error-prone parsing step by adding the member or the label
directly to the card object.
We also added support for `Tab` to completion on our textComplete
component.
Closes#342