Make SettingStore send messages on modification.
Add new settings.
Adjust default setting values.
Implement settings fragment.
Add green checkbox.
Make project selection for new time entries optional.
Make mobile tag optional.
Add idle notification.
Implement back stack for drawer navigation.
Merge branch 'roosmaa-settings-fragment'

Implement settings fragment and everything related to the new functionality.

Closes #92
Closes #98
Closes #99