Settings option: enable/disable automatic timer entries

[5TFN]

In my daily time tracking routine, I prefer to just assign a certain amount of time to a project/task and add a comment to it.
I actually never use timers.

It would be nice if the timer/automatic entry could be enabled/disabled as an option in the settings.
In case it is disabled, the start-timer "play icon" in the UI could be swapped to a "+"-icon to add the entry and the "Manual time entry" button can be hidden.

Also see my other suggestion which is related to this #298