feat: Task logger

[Woynert]

Added client side task logger:

• Log a task each time a new session is started
• List past tasks in a widget view
• Doesn't keep track of tasks from previous days
• Logged tasks persist through restarts
• File saved at ~..local/share/aboutlife/tasklog.json

In the future it might be useful to implement this logging at the server side. This data could be interesting to analyze.