GitLab

As it was unusable with GitKraken...

Remove default value from TextField

See merge request !1

- Only set `disabled` prop when component is a `button`

It was not the case when using custom components (other than "button")

- Better demo page
- Remove size difference between gradient and others
- Rename variant "link" to "text" and "flat" to "plain"
- Rename sizes and remove the "extra small" one
- Use theme for transitions, sizing and spacing
- Add background on hover for "text" and "outline" variants
- Remove CSS outline
- Add active styles

Due to the removal of useless HOC withStyles() in the previous commit