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.
Use github version of twitter-bootstrap-rails to fix firefox new tab problem
Set up Coveralls integration for test coverage.
Merge pull request #235 from pozorvlak/coveralls

Set up Coveralls integration for test coverage.
added specific commit to twitter-bootstrap-rails in Gemfile
Set up Rails coverage groups.
Filter spec files out of coverage reports.
Merge pull request #234 from Skud/bootstrap-middleclick

Use github version of twitter-bootstrap-rails to fix firefox new tab pro...
Merge pull request #237 from pozorvlak/coveralls

Coveralls
Merge pull request #233 from Skud/planted-at-bug

Planted at bug
Remove unused gems; don't load assets group in CI.
Remove explicit load of diff-lcs.

It's a dependency of rspec-expectations.
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.
Use unicorn instead of Thin webserver

This is in the name of eliminating unnecessary differences between
development and production. You must invoke unicorn with `unicorn`
rather than `rails s`. By default it listens on port 8080.
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.