Labels configuration

### Labels and button personnalization

Hi there, few labels were still in the html template, they are now available in config. My use case was to translate these leftovers to another language, as date format are already taken care of by angular date filter.
But could be usefull for simple label personnalization, ex : "Departure date".

* Move date & time field labels to configuration :
```
...
dateLabelHtml: 'Date',
timeLabelHtml: 'Time',
...
```

* Move clear button label to configuration :

```
...
clearLinkHtml: 'Clear',
...