Clean repo

script/sql/section_create/20.mixing.sql

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+-- [MIXING]
+
+CREATE TYPE MIXING_Model AS ENUM ('MIXED', '2COMP', 'FIFO', 'LIFO');
+
+CREATE TABLE MIXING
+(
+  Tank  VARCHAR(32) PRIMARY KEY REFERENCES TANKS(ID)
+, Model MIXING_Model NOT NULL
+, Value NUMERIC
+);