sql: simplify properties

schema.sql

@@ -105,23 +105,14 @@ CREATE TABLE IF NOT EXISTS attachement (
 	UNIQUE (part, priority)
 );
 
--- property unit
-CREATE TABLE IF NOT EXISTS unit (
-	id INTEGER AUTO_INCREMENT PRIMARY KEY, -- index
-	name TEXT NOT NULL UNIQUE,
-	symbol TEXT NOT NULL UNIQUE
-);
-
 -- part property
 CREATE TABLE IF NOT EXISTS property (
 	id INTEGER AUTO_INCREMENT PRIMARY KEY, -- index
-	name TEXT NOT NULL, -- property name (min V, ...)
-	unit INTEGER,
-	FOREIGN KEY (unit) REFERENCES unit (id)
+	name TEXT NOT NULL -- property name (min V, ...)
 );
 
 -- property value
-CREATE TABLE IF NOT EXISTS poperty_value (
+CREATE TABLE IF NOT EXISTS property_value (
 	id INTEGER AUTO_INCREMENT PRIMARY KEY, -- index
 	part INTEGER NOT NULL, -- the part
 	property INTEGER NOT NULL,