Void transaction feature
Add strikthrough css to voided transactions
print the word "void" before voided transactoins

I was worried that people might not know what the strikethrough meant,
and hope that the label will be a little more clear.
make void false by default

otherwise void is NULL, which doesn't make sense. We should assume all
transactions are NOT voided (void = false) unless they have been voided.

Because this is editing a migration, you'll have to run:
rake db:migrate:redo

It's generally better form to create a new migration, rather than modify
an existing one, but as we haven't deployed this yet, I'm going the lazy
route.
Exclude voided transactions from monthly reports

This will give us a more accurate picture of how many purchases /
investments we're making.

not the change to lib/tasks/rspec.rake

There's a little magic involved because we're using a database view to
back the monthly_report model, whereas generally models are backed by a
database table.
Merge branch 'feature/void_trans' into develop