Plasma 5.6 video

[Lucas S]

Hi

It is time for a quick update so here is the first version of the
Plasma 5.6 video https://youtu.be/q-nACSvivGU
After initial feedback on the plasma IRC channel, this is the list of
planned changes for the next video.

1.  Rework the end of the video, because now it ends rather unexpectedly.
2.  Update the "widget explorer" part
3.  Ivan are you ok with the "Activity Manager" part?
4.???
Feel free to post other suggestion/improvements, but please be quick :)