Add Request#can_send_money? helper
Improve homepage for send-money donors

* Send-money and send-books donations are now broken out on the homepage (“profile”).
* The donation partial has been adapted to render both, and is used for both.
* To support this, the Action view-model has been updated to support both list and detail contexts, and to handle send-money donations.
Add unsent fulfillments to profile page

Also show them on the volunteer index.
Put the with_prices scope on Book where it belongs
No-op tweak to Gemfile.lock

Bundler insists on doing this every time I run Rake. Upgrading to the
latest version (1.2.4) on all my dev machines and hoping they can agree
on this.