[gem] update Rails to 3.2.13.

This was a security patch. No code changes were needed.
[!!!][PostgreSQL] database switched from sqlite3 to PostgreSQL.

This necessitated a number of minor adjustments in the code.

`ExternalLink.default_scope` set so position will be used to sort.

Dropped the unused `Version.current_versions` scope since it wouldn’t work with Postgres without a bunch of changes to it.

Constrained `Wayground::Rememberer#get_random_token_string` to a max 127 characters to fit in the new default string data size.
[HtmlPresenter] ignore blank attributes
[HttpUrlValidator] common validator for http urls.
[PageMetadata][MetadataPresenter] move page metadata logic from instance vars and template to a model and presenter.

Moved most of the `@page_` metadata controller instance vars into the new PageMetadata class which is accessed through the `page_metadata` controller method/helper.

The generating of the `meta` tags in the `head` element of the main application layout has been moved to a presenter.
rich text editor: remove instance var; use template instead.

Removed the `@rich_text_editor` controller/view instance variable.

Instead, just add the needed javascript tags in the applicable template.
[Image][ImageVariant] models and controller for images with multiple variants.

Variants are things like scaled versions, thumbnail versions, squared versions, alternate formats (e.g., jpeg vs. png vs. svg).

Images can also be applied to the page metadata for use in Open Graph and Twitter Cards.
[gem] update gems.

Minor updates. Only one code change needed (cucumber fix because of a change to `have_selector` to match the entire text in an element, instead of allowing a partial match).

brakeman 1.9.4
capybara 2.1.0
cucumber 1.2.5
flay 2.2.0
flog 3.2.3
omniauth 1.1.4
omniauth-twitter 0.0.16
pg 0.15.1
rake 10.0.4
[EventsController] post notice on show action when event is tentative.
[CalendarMonthPresenter][ViewDouble] use safe_join in place of Array#join to join html_safe strings.
[HtmlPresenter] `anchor_or_span_tag` method.

Generates an `a` tag if using the given url for the href or, if the url is blank, generates a `span` tag with no href.
[EventPresenter] expanded and modified to support events_controller#show view.