Changes redirect on file upload

If the item form was nested inside a project, will redirect to the
project instead. Also, changes image resize to constrain and crop
the preview and thumbnail files respectively.
Changes preview partial to use image_tag helper
Changes item preview partial to widen anchor

Anchor tag encompasses entire figure. Also images are display: block,
and images inside class .item-preview have max- dimensions.
Updates item preview partial

If nested in a project, partial links to the nested item#show action.
Also adds a nav bar on project#show view, which initially contains
project title. (Same nav bar on project_item#show view will have item
parent thumbnails.)
Item partial conditionally assigns local vars to nil
Adds alt to item preview partial image
Changes project/item views to nest objects

In preview and item #show actions, items are only displayed if they are
the child of the current item. For preview#show, but current item is 'nil'
so it displays all the parentless (root level) items. For item#show, the
view displays child items of the current item being shown.
Adds parent & parent's siblings to item#show

If an item has a parent and is in a project, its show page will display
the next highest level of the project's hierarchy in the form of item
thumbnails. The parent thumbnail is highlighted.
Changes item#show css slightly
Better arranges item details, adds name as header
Nests item#new under existing items

The Item#new view is now under 3 routes: on its own, inside a project, and
inside an item. If it's nested in a project or item, the form will not
display the menu to assign the item to an existing project, and the create
action will assign the proper project_ and parent_ ids from the params.
Merge branch 'fixing-email'