make fixed time intervals configurable via settings.js

This pull extracts creation of preset (resp. fixed) time intervals and makes them configurable via `settings.js`. When new interval is being added the following has to be specified:

* `name`: the name of the interval
*  `from`: start time of the interval
* `till`: end time of the interval
* `label`: an i18n key to enable translated text (to be added under `i18n/<languageCode>.js`

Use `moment()` to create time intervals dynamically, e.g.
```javascript
{
    name: 'lastHour',
    label: _('timeSelection.presets.lastHour'),
    interval: {
        from: moment().subtract('hours', 1),
        till: moment(),
        mode: 'minutes'
    }
}
```