Allow Rails applications to override default views

The first time a template is rendered, Vanity checks to see if the path
'app/views/vanity' exists, and if so will load templates from that
location. Otherwise templates are loaded from the gem as normal.

This commit also adds a Rails generator to put copies of the original
templates into 'app/views/vanity'.
Drop google groups in favor of stackoverflow tag.
Remove un-used test/experiments folder.
Remove deprecated vanity command option.
Remove deprecated vanity upgrade command.
Ensure rails dummy has secret_key_base if necessary.
Remove unneeded test support for Rails2.
Fix miss-labeled tests.
AR metric test should run in AR test environment.

* Don't needlessly create new connections to the DB, can create deadlocks.
Fix ActiveRecord Metric to use newer find syntax.

Fixes #228.
Bump version to 2.0beta4 for AR fixes.
Add `custom_templates_path` configuration option.

Vanity.playground now has a configuration option,
`custom_templates_path`, which is used as a search location for custom
templates (to override the default ones in the gem).

By default this option is set to `app/views/vanity` in order to work
with Rails.
Merge pull request #229 from rsslldnphy/override-templates

Allow Rails applications to override default views