many minor fixes, miscellaneous beautification

fof_get_feeds() now does full initialization of its returned array, quelling notices and setting reasonable defaults for all entries.

Relative-timestamp strings of many days now round to weeks and years.

Most of sidebar.php was rearranged to consolidate some rendering and pretty-up the emitted html.

Some URLs are now constructed in a more consistent manner, using new function fof_url().

Default items.php view is now 'paged', rather than 'all'.

Moved some repeated javascript from attributes into fof.js functions.

Ajax requests generated in fof.js now uriencode tag parameters.

favicon service request now encodes url.

Fixed typo in fof_db_get_item_count() from pdo rewrite.  However, it seems to tally incorrectly for multiple tags.  I attempted to rewrite it, but SQL is not my bailiwick, so the original is still in place.

Generalized fof_db_get_unread_count() into fof_db_tag_count(), removed wrapper function fof_get_unread_count().

Fixed typo of item_target pref handling in fof_render_item().

Output of fof_view_title() is now more conversational.

Removed unused function fof_db_item_has_tags().