FR: add more configuration options for inputs in UI form

[Sulomus]

I have found out that you are not able to set for example min and max limits to numeric input in UI_form (and other people were asking for this too). Which makes it harder to use in many cases because it requires to manually check if the limits are not set.

I have found out that also few more thinks could be really nice if they were added. Whole list below:

1. Add the option for numeric input in UI_form to set MAX and MIN limits
2. Option to add custom onNonValid messeges.
3. Add option to set custom placeholders

I have been successful in making my own form with the UI_template node which gives me some basic idea of how the final code have to look to work. idk if it can help in creating the new features or if it will be useful to anyone:

    <md-input-container class="md-block">
      <label> Required humidity </label>
      <input 
        type="number" 
        ng-model="humidity" 
        min="48"
        max="52"
        required
        placeholder="Please enter humidity between 48 and 52%"
        oninvalid="this.setCustomValidity('Value must be between 48 and 52%')"
        oninput="this.setCustomValidity('')" --this is required or if the user inputs value again it will still be showing the error message
      />
    </md-input-container>

I would be more then happy to create a pull request and contribute to this project but my knowledge is fairly limited. I have looked into some tutorials on how to create your own nodes but still don't feel confident enough (but I am more then open to if someone would walk me through it! ).