Moves get_content to Item instance method
Adds new item#tags assignment

Item method #tag_names plucks tag names and joins them with a specified
separator (space by default). Method #tag_names= splits a string by spaces,
then maps each element (a tag name) to Tag.first_or_create (using the item's
user_id as the new tag's user_id). Both #tag_names= and Tag's before_save
downcases the name.

Also moves get_content back to helper method because it relies on image_tag
(and would still rely on erb's html escape if it were tagged manually).
Conditionally appends ... to item text summary
Fixes broken conditional statement in item.rb
Separates tags by commas, so they can contain spaces
Adds more seed data
Changes default tag separator to match input string
Fixes extra ul/li in tag#show
Styles item sidebar to be lighter.
Moves left navbar into controller layouts
Adds Time Zone to user model
Fixes wrong timezone issue
Adds default tz to application.rb
Fixes broken validation on new tag on item create
Revises layout

Root layout has 3 columns of uncategorized files, upcoming reminders, and
favorites.

Project and Item layouts put their nav bars in a block that the application
layout yields to.
Adds project index page for current_user

Layouts adjusted to account for a project controller page without any current
project id. On index load, fires off a query to get user's projects with a count
of its items and total reminders.

Also simplifies some css without changing much.
Changes SQL to only count reminders in next 7 days
Adds a coalesce to catch null values
Fixes broken layout when not viewing an item
Adjusts CSS, especially user search.

Also adds a padded-main class that simply adds padding to a section directly
below the header. (Other sections sit flush against it.)