Modifications to login box formatting

Following on from https://jira.nuxeo.com/browse/NXS-6331

Width

The width doesn't seem to be working correctly, the width of the box does not change, it always set on 500 (from the max-width of the div)  

> Delete this option TBC 

or

-> Make width changeable between 300 and 1000 / Or delete this option TBC 

(-> Add this info to ? hover )

Button background colour 

This always display the original blue colour 

-> Add box to set 'Button Background Hover Color' (same as Button 'Background Color')

Padding 
1. If the logo you’re using is taller than the default logo, the layout eats up the padding so the space under the login button becomes very small.
-> The padding should stay consistent

-> Constrain size of logo to less than 300px by 300px

-> Add this info to ? hover 

Image guidance 

For the bg image fill, it is currently on 'contain' and fills the space only if it is the correct proportions, the yellow in the picture is the coloured background, the image should cover the entire background

-> Suggest dimensions and add this info to ? hover  (TBC)