Lv2: Use port-property "logarithmic"

This also adds more min/max checks, mostly for logarithmic scales.
Since this raised some warnings for logarithmic CV ports, the CV
metadata is now also read (but CV ports are still not supported).

include/Lv2Ports.h

@@ -108,6 +108,8 @@ struct Meta
 	Flow m_flow = Flow::Unknown;
 	Vis m_vis = Vis::None;
 
+	bool m_logarithmic = false;
+
 	bool m_optional = false;
 	bool m_used = true;
 

include/PluginIssue.h

@@ -32,18 +32,27 @@
 //! LMMS Plugins should use this to indicate errors
 enum PluginIssueType
 {
+	// port flow & type
 	unknownPortFlow,
 	unknownPortType,
+	// channel count
 	tooManyInputChannels,
 	tooManyOutputChannels,
 	tooManyMidiInputChannels,
 	tooManyMidiOutputChannels,
 	noOutputChannel,
+	// port metadata
 	portHasNoDef,
 	portHasNoMin,
 	portHasNoMax,
+	minGreaterMax,
 	defaultValueNotInRange,
+	logScaleMinMissing,
+	logScaleMaxMissing,
+	logScaleMinMaxDifferentSigns,
+	// features
 	featureNotSupported, //!< plugin requires functionality LMMS can't offer
+	// misc
 	badPortType, //!< port type not supported
 	blacklisted,
 	noIssue