Update timestamp format

Summary:
Provide also the date, using the same format than system logs.

Plan is to currently hardcode the value, and move to configuration
if there are opinions for another format.

Reference:
https://docs.python.org/3.6/library/datetime.html#strftime-strptime-behavior

Fixes T1146.

Test Plan:
Run the new client, wait for a notification:

[Jan 31 20:40:02] <Nasqueron/nasqueron> dereckson created D898: Provide a minimal installer.

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T1146

Differential Revision: https://devcentral.nasqueron.org/D899