Add Custom Time Range

[shafy]

Currently, users can only select from different predefined time ranges. I think it would be useful to allow users to set custom time ranges additionally.

I'm not sure yet how to best implement this UI-wise. One idea could be to show it as an additional option in the date range dropdown, and when the user clicks on it they will see two date fields to set a range (e.g., below the predefined date ranges or in a new pop up). Another idea could be that the custom date range inputs are shown by default.

For the first iteration I wouldn't go with a custom JavaScript date picker, but use the default HTML <input type="date">. I think that it looks good enough and going forward will also be improved.