Add PostgreSQL support

Therefore add migration scripts and default connection settings. Also
add a draft chapter in the documentation about how to setup the database
. Make HSQLDB the default for integration tests.

src/main/resources/database/postgres/V1_0_0__init.sql

@@ -0,0 +1,45 @@
+--
+-- This file contains the basic initialization of the financer schema and basic init data
+--
+
+-- Account table
+CREATE TABLE account (
+    id BIGINT NOT NULL PRIMARY KEY GENERATED ALWAYS AS IDENTITY,
+    "key" VARCHAR(1000) NOT NULL, --escape keyword "key"
+    type VARCHAR(255) NOT NULL,
+    status VARCHAR(255) NOT NULL,
+    current_balance BIGINT NOT NULL,
+
+    CONSTRAINT un_account_name_key UNIQUE ("key")
+);
+
+-- Recurring transaction table
+CREATE TABLE recurring_transaction (
+    id BIGINT NOT NULL PRIMARY KEY GENERATED ALWAYS AS IDENTITY,
+    from_account_id BIGINT NOT NULL,
+    to_account_id BIGINT NOT NULL,
+    description VARCHAR(1000),
+    amount BIGINT NOT NULL,
+    interval_type VARCHAR(255) NOT NULL,
+    first_occurrence DATE NOT NULL,
+    last_occurrence DATE,
+    holiday_weekend_type VARCHAR(255) NOT NULL,
+
+    CONSTRAINT fk_recurring_transaction_from_account FOREIGN KEY (from_account_id) REFERENCES account (id),
+    CONSTRAINT fk_recurring_transaction_to_account FOREIGN KEY (to_account_id) REFERENCES account (id)
+);
+
+-- Transaction table
+CREATE TABLE "transaction" ( --escape keyword "transaction"
+    id BIGINT NOT NULL PRIMARY KEY GENERATED ALWAYS AS IDENTITY,
+    from_account_id BIGINT NOT NULL,
+    to_account_id BIGINT NOT NULL,
+    "date" DATE NOT NULL, --escape keyword "date"
+    description VARCHAR(1000),
+    amount BIGINT NOT NULL,
+    recurring_transaction_id BIGINT,
+
+    CONSTRAINT fk_transaction_from_account FOREIGN KEY (from_account_id) REFERENCES account (id),
+    CONSTRAINT fk_transaction_to_account FOREIGN KEY (to_account_id) REFERENCES account (id),
+    CONSTRAINT fk_transaction_recurring_transaction FOREIGN KEY (recurring_transaction_id) REFERENCES recurring_transaction (id)
+);