Add initial SQL schema for creating SQLite DB

schema.sql

@@ -0,0 +1,17 @@
+CREATE TABLE IF NOT EXISTS tag (
+	id INTEGER PRIMARY KEY AUTOINCREMENT,
+	name TEXT NOT NULL UNIQUE
+);
+
+CREATE TABLE IF NOT EXISTS button (
+	id INTEGER PRIMARY KEY AUTOINCREMENT,
+	file TEXT,
+	checksum TEXT
+);
+
+CREATE TABLE IF NOT EXISTS button_tags (
+	fk_tag INTEGER,
+	fk_button INTEGER,
+	FOREIGN KEY(fk_tag) REFERENCES tag(id),
+	FOREIGN KEY(fk_button) REFERENCES button(id)
+);