Use ShellGenericContainer to implement a fully dynamic layout
for the application well. It's still fixed to 4 columns by default,
but no longer requires a fixed width to be passed in on start.
With another chunk of work, it could likely try to adjust to
the case where we can only fit fewer than 4 items in the well.
Remove the border highlighting on mouseover, since that caused
reallocations, and the grid layout isn't trivial.
Delete the unused shell_global_get_word_with function.
This patch is a near-total rewrite of the Dash. First, the dash
code moves into a separate file, dash.js.
Inside dash.js, the components are more broken up into separate
classes; in particular there's now a Pane class and a MoreLink
class. Instead of each section of the dash, when activated,
attempting to close all N-1 other sections, instead there
is the concept of a single "active pane", and when e.g. activating
the More link for documents, if we know there's an active pane
which happens to be the apps, close it.
Many redundant containers were removed from the dash, and all
manual width, height and x/y offsets are entirely gone. We move
the visual apperance closer to the design by using the view-more.svg,
etc.
To complete the removal of height/width calculations from the dash,
we also had to do the same for GenericDisplay. Also clean up
the positioning inside overlay.js so calculation of children's
positioning is inside a single function that flows from screen.width
and screen.height, so in the future we can stop passing the width
into the Dash constructor and call this once and work on screen
resizing.
