Preserve sort order of list elements

Saving items with partially fetched fields from DB will lead to overwrite of 'sortOrder' field with max value for this field in the list.

Changed behavior:
check for 'sortOrder' field presence in schema.
Admin UI elements for tracking fields
Use buttons where possible for accessibility

Also added a proper focus state to buttons for better visual feedback
preview buttons should use the default button style
Displaying tracked metadata in the Admin UI
Added StorageJS dependency
Removed storage from Master branch

So other fixes can still be done
Added syntax highlighting
alt. implementation of #634, sortOrder type detection fix
Can toggle display of created / updated dates in list view
Added syntax highlighting + white chars
Adding order UI for tracking date fields
Implementing proper ascending / descending UI for tracking sort
Fixed bolded text
Improved white space in production mode, fixes #642
More appropriate usage of mongoose as keystone.mongoose.
Sync with original Keystone.
Types.LocalFiles fixed functionality on sort / upload / delete.
Merge pull request #651 from grabbou/feature-better-readme

Better readme fixes #575
Merge pull request #649 from Darkin8/master

Types.LocalFiles fixed functionality.