add DataStore class to create sqlite3 db

DataStore.py

@@ -0,0 +1,41 @@
+
+import sqlite3
+import os
+from datetime import datetime
+
+class DataStore:
+    def __init__(self, dbfile):
+        if not os.path.exists(dbfile):
+            self.createdb(dbfile)
+        self.conn = sqlite3.connect(dbfile)
+
+    def __del__(self):
+        self.conn.close()
+
+    def createdb(self, dbfile):
+        conn = sqlite3.connect(dbfile)
+        c = conn.cursor()
+        c.execute('''
+CREATE TABLE projects (
+    id INTEGER PRIMARY KEY,
+    name TEXT
+)''')
+        c.execute('''
+CREATE TABLE tasks (
+    id INTEGER PRIMARY KEY,
+    projectid INTEGER,
+    name TEXT,
+    UNIQUE (projectid, name),
+    FOREIGN KEY (projectid) REFERENCES projects(id)
+)''')
+        c.execute('''
+CREATE TABLE hours (
+    date TEXT,
+    taskid INTEGER,
+    seconds INTEGER,
+    PRIMARY KEY (date, taskid),
+    FOREIGN KEY (taskid) REFERENCES tasks(id)
+)''')
+        conn.commit()
+        c.close()
+        conn.close()