Drop the intro animation

While it has a certain nice branding value if executed perfectly (which we are
a bit off still), the intro animation does more damage than help.

Getting Started was initially designed to be opt in, but the way we start the
playback for eveyrone right after launching the session (and sometimes after
yelp actually comes up in the background), the experience is extremely
confusing. The combination of forced passive consumtion, unpolished launch and
complexity of the animation just makes the start of Getting Started unhelpful.

We should drop the intro and stick to the inline videos and image guides inside
yelp.

https://bugzilla.gnome.org/show_bug.cgi?id=703999
Remove player

It's unused
Use the distro name in the 'Start' button

Parse /etc/os-release to find the name of the distribution, and
use it instead of 'GNOME 3'. If we don't find that file, fall back
to using 'GNOME 3'.

https://bugzilla.gnome.org/show_bug.cgi?id=695692