Initial import of lyx-1.5.3, latest stable version that uses the QT4

Initial import of lyx-1.5.3, latest stable version that uses the QT4
toolkit.

LyX 1.5.0 is the culmination of 15 months of hard work since the release of
the LyX 1.4 series. We sincerely hope you will enjoy the result. The changes
are too numerous to summarize in a few words, but initial unicode support is
the flagship among the new features.

As usual with a major release, a lot of work that is not directly visible
has taken place. The core of LyX has seen more cleanups and some of the new
features are the direct results of this work.