Add invoice view, bugfixes and improvements

[rnixx]

This PR includes the following changes:

• Ajaxify cancel bookings.

• Fix comment editing in plone 5.

• Only display cancel booking action if booking not already cancelled.

• Fix error in the order detail if the product no longer exists (#20).

• Do not exclude reserved bookings by default from billing. This resolves inconsistenty introduced with https://github.com/bluedynamics/bda.plone.orders/pull/39 and addressed at https://github.com/bluedynamics/bda.plone.orders/issues/45.

• Introduce ProtectedOrderDataView and use as base for DirectOrderView and DirectInvoiceView.

• Add invoice view.

• Remove duplicate Translate class from bda.plone.orders.browser.contacts.

• Rename OrdersContentView to ContentViewBase. Provide B/C alias. Introduce view configuration properties do_disable_border, do_disable_left_column and do_disable_right_column.

• Introduce OrderDataView base class for views dealing with single order data.

[rnixx]

Improves the situation in any case, done as PR for traceability reasons, thus I'll merge on my own.