Add epanet input schema

sql/section_create/18.sources.sql

@@ -0,0 +1,11 @@
+-- [SOURCES]
+
+CREATE TYPE SOURCES_TYPE AS ENUM ('CONCEN', 'MASS', 'FLOWPACED', 'SETPOINT');
+
+CREATE TABLE SOURCES
+(
+  Node VARCHAR(32) PRIMARY KEY REFERENCES _NODE(ID)
+, Type SOURCES_TYPE NOT NULL
+, Strength NUMERIC NOT NULL
+, TimePattern VARCHAR(32) REFERENCES _PATTERN(ID)
+);