If Member has Overdue tools, prevent Picking Up new tools

[sboligitz]

This still needs a bit of thought.

The general idea is to prevent people from Picking Up new tools if they've got overdue tools to return. We'd need to think through:

• How many items can someone have out at once in general?
• How many items can be overdue before new holds are blocked (assumes only 1)
• How do we notify the member from the tool detail page that they cannot put on Hold because they have things overdue?