TT#146800 support decimal VAT rates

Change-Id: Ibdb0b3f76e40b4d4699ee784a4f04a2e065f1c38

db_scripts/diff/15704.down

@@ -0,0 +1,2 @@
+use billing;
+alter table contracts modify column vat_rate tinyint(3) not null default 0;

db_scripts/diff/15704.up

@@ -0,0 +1,2 @@
+use billing;
+alter table contracts modify column vat_rate decimal(14,6) not null default 0;