Make `academic_title` field optional

Add a config setting to make display of the "Academic Title" input field
(in contact edit forms) optional.

(This doesn't affect contact view, as the name displayed there is
determined by the "Individual Display Name Format" template instead.)

This is a minimal approach, adding just the title setting. Perhaps it
might be preferable to add a full set of options for disabling the other
name fields as well, while at it?...

(We are willing to do that too, as it shouldn't be too hard, and we have
users for that as well -- but we need some consensus about the right way
for handling this.)

The setting is placed in the "Display Preferences", next to the
"Individual Display Name Format". However, it could be placed next to
"Editing Contacts" (also in "Display Preferences") as well -- it's
somewhat related to both...
Introduce new `communication_style` field for Contacts

Add new field in the Communication Preferences block, mostly for driving
the new conditional greeting templates. (Though other uses are
possible of course.)

The Communication Style field is implemented as radio buttons defined
through an option group (pseudoconstant), similar to the Gender field.
Unlike Gender, it has a default value assigned automatically for new
contacts.

The field is placed just above the Email Greeting, Postal Greeting, and
Addresse controls, as it's meant to be used as a kind of master switch
driving the various greeting templates. Just like the Prefix/Suffix
fields in the name block for Individual contacts, the Communication
Style field is automatically hidden from all forms and views if no
option values are defined for the field.

While this field is mostly meant to be used as a token in greeting
templates, currently it's not available as {contact.communication_style}
(option labels), but only as {contact.communication_style_id} (numeric
values), because of http://issues.civicrm.org/jira/browse/CRM-13161
and/or related issues. This should be fixed before release.

The database field comes with an index, like all(?) pseudoconstant
fields. Presently the index is not used much (probably the only place
being deletion of existing option values); but this is likely to change
when more functionality is added around this field in the future.
(Search etc.)

The handling of the new field throughout the CiviCRM code base should be
mostly complete. We deliberately punted on some of the obvious, larger
pieces of functionality (search, import, profiles) for now, as they
would require considerable additional effort, so we treat them as extra
features to be implemented seperately upon need. We tried to be complete
with all smaller bits (mostly by grepping for `gender`, which requires
similar handling in most places...); but we might have omitted some,
and/or done some that aren't actually necessary -- it's rather hard to
tell sometimes what a particular piece of code is all about...
Add configuration UI for Communication Style options

Add a page in the Communication Preferences, using the generic Option
handler.

The menu entry is added above the entries for Email Greeting Formats,
Postal Greeting Formats, and Addressee Formats, just like in the actual
contact forms and views.