Correct the spelling across the *entire* tree, including translations,
comments, etc. It's easier that way.

Even the places where it's not exposed to the user, such as tests, so
that we learn how is it spelled correctly.

Previously, the action was only passed as the first command line
argument to the dispatcher scripts. Now, also set it via the
"$NM_DISPATCHER_ACTION" environment variable.

The main purpose is to have a particular, nm-dispatcher specific
variable that is always set inside the dispatcher scripts.
For example, imagine you have a script that can be either called by
dispatcher or some other means (manually, or spawned via
/etc/NetworkManager/dispatcher.d/11-dhclient).  Then it might make
sense to differenciate from inside the script whether you are called
by nm-dispatcher. But previously, there was no specific environment
variable that was always set inside the dispatcher event. For example,
with the "hostname" action there are no other environment variables.

Now (with version 1.12), you can check for `test -n "$NM_DISPATCHER_ACTION"`.

(cherry picked from commit ce9619047c5daac9a006d16d07453d50e0520e71)

although they are deprecated and unused, document them.

This gives the templates a chance to do something extra clever with the
formatting. The templates, of course, choose not to :(

The temaplates capitalize the names if they wish.

Also added documentation for the new CONNECTIVITY_STATE environment
variable, that will also be avaiblable in those hooks.

https://bugzilla.gnome.org/show_bug.cgi?id=768969

This improves the HTML rendering.

But it also causes a lot of non-resolvable linkends warning when rendering a
separate manual pages into roff/mman. The messages are harmless, but still
a bit ugly.