Use OPENSCAD_LIBRARY include path only if it actually exists.
Add static dependency builds for Qt5 and QScintilla2.
Use blacklist approach to include library dependencies.
Add curl and libffi-dev to Debian dependencies.
Remove dependency to libpng when building freetype.
Include swrast_dri driver.
Add packages needed for static Qt5 builds.
Update to Eigen 3.2.2, boost 1.56, cgal 4.4.
Use https download link for gmp.
Build fontconfig with --prefix=/ to let it pick up system data.
Merge pull request #923 from openscad/linux-build-update

Update build scripts