online applications: ignore tombola
disable tombola

Remove all the code to handle the food fair tombola apart
from the model definitions to avoid changing the databse
and to not loose previous information.
online applications: tweak text + max 2 n_spaces
online application: users must positively select stall type

Add undefined option to the stall type list so people will
have to positively choose a stall type in order to complete
the form.
apply.html: remove deprecated block of text
thank-you-email.html: remove line about tombola
apply.html: scroll to the stall type when it changes

In order to see the rest of the form when it appears, use the
JavaScript obj.scrollIntoView(true) method to scroll it to the
top of the browser window when the stall type changes.
online applications: replace n_spaces with mc_stall_option

The Market & Crafts stalls now follow a different scheme, with
either indoors or outdoors options.

* extra/models.py: add mc_stall_option field to extra_stallevent
  table which is an enumeration of the 3 possible options
* extra/forms.py: replace n_spaces with mc_stall_option in
  StallForm as this is now the new way to define the stall set-up
* extra/public/apply.py: show the stall option instead of the
  number of spaces in the confirmation e-mail
* templates/public/apply.html: tweak text, prices and replace
  spaces with stall options
* templates/public/thank-you-email.html: replace n_spaces with
  mc_stall_option
* templates/public/thank-you-email.txt: fix sender name at the
  bottom of the email
invoices: fixup n_spaces vs mc_stall_option

* extra/forms.py: do not clean-up the value of n_spaces
* extra/models.py: set default n_spaces to 0
* extra/views/mgmt.py: fix invoice details using the new M&C
  stalls amounts
* templaces/cams: do not show n_spaces if 0 and show
  mc_stall_option if not none + fix typo in
  invoice_hard_copy.html (dangling /div)
fix stall fields in add/edit invoice templates

When defined, show n_spaces, n_tables, mc_stall_option and
plot_type in add_invoice.html and edit_invoice.html
mgmt.py: fix stall invoice amount + tidy-up

Fix stall invoice amount in AddInvoiceView for both
stall types (M&C and FF) using hard-coded dictionaries.

Also fix code formatting and tidy-up details put in
invoice html page.
rename invoice hard_copy -> html

* mgmt_urls.py: rename hard_copy -> html
* mgmt.py: rename InvoiceHardCopyView -> InvoiceHTMLView
* templates/cams: rename with html instead of hard_copy
extra/views/mgmt.py: fix invoice details again
StallEvent: fix M&C stall options
apply.html: update text and description of M&C options
apply.html: fix links to external documents