lyxbuild: copy entire contents of --user-dir arg

--bind and --prefs are deprecated.
Remove the PPAs

The advantages are that there are fewer dependencies and that
we can now test on Ubuntu 14.04, which the PPAs do not yet support.

The LyX PPA was not being used. I thought I might use it for
build-dep but I ended up apt-get installing the dependencies manually.

The R PPA was only used to test against the latest R version
instead of the default repo version.