Data views grid layout: Add a density view option

[jameskoster]

In Grid layout, it can be useful to adjust grid density ad hoc. For example in pattern management, if you're browsing 'larger' patterns such as those in the 'Pages' category then a lower grid density can be beneficial:

Whereas it may be preferable to browse 'smaller' patterns with greater density:

By providing a view option that enables users to control density we can improve the management experience in Grid layout.