Timer (Clock In and Clock Out) cannot record multiple intervals

[jiriyu98]

The timer works well for tasks that have only one interval but it cannot record multiple intervals. However, it seems like in most cases, one task cannot be done at once and therefore needs several intervals to record how much time we spend on it.

I am wondering if the Timer functionality can be improved to support the following features:

1. Automatically record Clock In and Clock Out
2. For tasks that have multiple intervals, it can correctly record all the intervals they have.

Refs: 49229bd, #77