Pop "css_id" to stop it being added as a "css-id" attribute

Changed ```BaseInput``` so that it pops the "css_id" from kwargs.

Previously it was updating the "self.id" and then being flattened to "css-id" leading to an odd attribute.

Before:
```html
<input other-attributes id="new-submit-id" css-id="new-submit-id">
```
After:
```html
<input other-attributes id="new-submit-id">
```