Add utility function find() in array-utils
Set 'authors' instead of 'totalAuthors' in each layout cell

The list of authors is needed to determine which circle
corresponds to which author on hover.
Move constants from layout to filter-constants
Rename 'tile' to 'tilePosition'

The same variable 'tile' was used for the tile position record
and for the d3.js tile object. I renamed the variable for the
first usage.
Publish the tile node in 'over-tile' and 'out-of-tile' events

Previously, the parent shape object was published instead,
making it impossible to position the author card below the
hovered tile.
Set the position of the author card below the hovered tile
Center the author card below the hovered circle

This new feature is intended to keep the card more closely related
to the related author circle, but it has side effects on the edges of
the screen and when the author card is displayed on top of the menu.