Flesh out item lend page and supporting JS

Flesh out the lend update form. Create all necessary inputs for fully updating a
lend.

Write JS to properly support the form. By default, the form will display
"date" and "datetime" inputs. The JS will probe the browser to see if it
supports "date" or "datetime" inputs and, if not, fiddle with the form
appropriately.

Run both existing and new JS through the JSLint program and eliminate all
warnings. Place JSLint comments in file so file can easily be de-linted again in
the future.
Polish /{item,tag,lend}/<id> pages.

Add links to each page leading to the update/edit and delete pages. All links
are contained within `p.controls` tags.

Improve wording of headlines and paragraphs. For example, make header state
"Notes About This Tag" instead of "Notes".

Convert some headers into <p> tags. Also show less information by default. For
example, only show "tags attached to this item" if tags are actually attached to
that item. These two changes make it much easier to find useful information
about an item. Less time is spent wading through useless information and
excessive headers.