improve automatic view-mode adjustment, so it gets triggered whenever the test-view table is to large vor the viewport (not as before on foxed break points in window-width). gets checked after every booklet load and window-resize, which should be the main reasons for changes in the table's width.

other reasons can change the table's with, like very long title of the featured unit, but in this case we don't want to wrap the whole view actually.

Bump websocket-extensions from 0.1.3 to 0.1.4

it was subscribed one time for each unit, which lead too very many calls of getUnitContext

Bump npm-registry-fetch from 4.0.3 to 4.0.5

Bump lodash from 4.17.15 to 4.17.19

I anticipate that at one point https://github.com/iqb-berlin/testcenter-frontend/issues/53 will be solved, so in most serious error-casses, we would leave app and goto an error page. Since this functionality is missing, the error-handling at this point can only lead to clear messages, but let app continue to function (which does not make much sense at all).

closes https://github.com/iqb-berlin/testcenter-frontend/issues/165 for now.

make it possible to show/hide group-columns (in anticipation of the feature request to display more then one group in one minitor wwhich will, I bet, come)

refactorment of `findUnitByName` to display medium (groupe) view correctly in deeply nested testlets