Allow new members to sign up

[MarkBennett]

We'll need to figure out a process for new members to sign up, collect membership fees and to keep a record of our active membership.

In the future, we should also have a process to renew memberships and expire those that have lapsed.

We also need to decide if we want to collect membership fees or not.

[abramhindle]

One option is to pay at meetings and AGMs to the treasurer. This avoids the pain of paypal messing with a bank account. Paypal and similar entities enables faster payment from your membership.

[SteveReiter]

Related to #18