+option to fetch dw-nonfree; default no

Also remove option to specify a bare github user on the command
line as a single argument; keeping this interface isn't such a
great idea now that we have a second command line option.
(cherry picked from commit 0e4c8edec8c7e3550bd707fd22f1d1c80fda16d6)
consistency: set $LJHOME once & use it thereafter
(cherry picked from commit ace3f969ef3dc650fa37f7615037ae545d6c7671)
clone dw-nonfree only if --dw-nonfree is set
(cherry picked from commit 45b6ac1458c69c5ee39a0920f6b4e42e45148a3e)
mkdir $LJHOME if it isn't there already.
(cherry picked from commit b3683802fc894284874608de1e89ab3a724a871b)
rm tempfile workaround; clone dw-free to $LJHOME

From the discussion here:
https://github.com/dreamwidth/dw-free/pull/355#discussion_r3920545
it's not common or encouraged for people to put dw-free directly
into $HOME.  Thus, we can remove the tempfile dance and simplify
the code a bit.
(cherry picked from commit ce192ecabbe2ab968cb15cced02e6962610a1b4c)
+messaging re use of dw-nonfree.

Also, clean up a few messages to bring lines under 72 chars.
(cherry picked from commit 56f9d2ec840ed220ded75a801ff57b0efebbaa75)
slight messaging clarification.
(cherry picked from commit fa8aef2f57d7bcd4f37f7b1a541c71a47eff5700)