Added form widget "TimePicker" to Backend.

Example "fields.yaml":

```Yaml
fields:
    time:
        label: Time
        placeholder: Time
        type: timepicker
        autoclose: true # (autoclose timepicker: true or false, Default: true)
        donetext: "Done" # (text for "Done" button. Not use if autoclose is true)
        placement: "bottom" # (popover placement: "top", "bottom", "left" or "right". Default: "bottom")
        align: "right" # (popover arrow align: "left" or "right". Default: "rigth")
```