Add LV2 header location compatibility

Add rdfs:comment to indicate factory preset

Fix build dependency of plugin presets

Update git clone URL

Update README.md

typo

Add icon

Fix symbol visibility

Improve x-builds (pkg-config variable)

fix ttl (missing semicolon)

Rename cs_VERSION to controlfilter_VERSION.

The name of this variable needs to match the name used for the submodule
in x42-plugins, in order for the rule that generates gitversion.mak to
work correctly. If the name doesn't match, building x42-plugins from a
tarball will result in it trying to figure out the version based on the
Git tag and failing.