bugfix: don't say 'not yet set' in planting form

PT: https://www.pivotaltracker.com/story/show/51457917

Maco found this. The problem was that if you had a blank planting date,
and then re-edited the planting, it would say "not yet set" in the form
field, then die when it later tried to convert that to a date.

I replaced Miles's planted_at_string stuff in the model with a simpler
parse_date method in the application helper.
Merge pull request #233 from Skud/planted-at-bug

Planted at bug
Only use the 'debugger' gem in development.

Installation was failing on Travis CI causing spurious failed builds, so
we don't want it under the test environment. I reckon we don't want it
in the production environment anyway.
Don't load the "development" gem group on Travis CI.
Allowing Miles to drive.
Tests and sketch implementation of not_staff scope.

It doesn't work and we don't yet know why :-(
Give new users a free account.
Updated .gitignore to include coverage files anywhere in the directory tree.
Create free account type if it doesn't exist; fix tests.
Remove "if account_type" checks in Account.

 - remove account_type_string method
 - simplify paid_until_string.
Use ActiveRecord methods for not_staff join code.

 - set member.account_type directly in tests, because changes to
   member.account.account_type weren't being persisted.
Rake task to give everyone free accounts; fix descriptions.
Fix pending tests in views/shop/index.

We needed to stub out current_member, not current_user.
Deleted unused admin_helper_spec.rb
Slightly simplify tests for not_staff scope.

There's no reason to set a location on the test member.
Documented reason for using south_pole_member in tests.
Added default account type of "Free" in config/applications.rb
Removed redundant logic for free account type in apps/views

A couple of pages were testing for an account type and displaying
"Free" if account type was nil. Now that we've ensured every account
has an account type, this is no longer necessary.
Updated tests to test for the default account type.

Tests used to check that the default account type was always "Free".
Now that we have a default account type as a config variable, the
tests test to see the default account type matches the value of that
variable.
Updated script/deploy-tasks.sh to include nil_account_type task.

We added a rake task to ensure all account have a Free account
type. This ensures the new nil_account_type rake task will be run
at deploy time.