Add textarea styling. Allow to set border for all input types

[galulex]

1. Allow users to overwrite border for all inputs by overwriting border variables.
2. Add styles for textarea

Before

After set the $picnic-border-weight: 3px and $picnic-border-color: orange

[franciscop]

I cannot test the pull request right now, I'm sorry for the delay. It looks a nice feature to have so I'll check it ASAP

[franciscop]

It's quite an impresive update. However there are small issues with the new radiobuttons and checkboxes. I'll fix them and release it as the 2.2 version