Connectivity widget: make small comment fixes
Connectivity widget: move response handling out of table creation

This change is made to separate the concerns "request response handling"
and "table creation". Moving the response checking code directly into
the handler seems more logical to me and fits more into the pattern how
requests are handled in other places of CATMAID.
Connectivity widget: simplify removal of UI elements

There is no need to refer to all UI elements explicitly to remove them.
It is much simpler to call empty() on the container.
Connectivity table: support "side by side" and "successive" table layouts

If the toggle checkbox is unchecked, the tables are shown one after the other,
otherwise the display is as before. To do this, the "container table" had to be
removed. Both tables are now in a separate div container which is floating to
the left. The toggle basically sets the width of these container divs to either
100% or 50%.

This relates to issue #600.