Reduce strictness of item matching when filtering items

Instead of requiring the pattern to occur as a complete
phrase within one of the main item metadata fields,
split the pattern into whitespace-separated clauses
and require each clause to match one of the metadata
fields.

The shell command parsing is re-used to parse the
search pattern to stricter matching can be achieved
using quotes.

eg. 'acme goog' will now match an item titled
 'ACME Ltd. - Google Account' but '"acme goog"'
would not.
Fix web app failing to display items in Chrome

The web app was detecting its environment as a Chrome
extension when run in Chrome and trying to use the Chrome Extension
Dropbox auth driver.

Make the test for the Chrome extension environment stricter
by testing for window.chrome.extension
Exclude folders and other 'system' item types from the main item list