luci-base: add ability to hide section titles

luci-base: add ability to hide section titles

The rationale here is that tabbed CBIMaps were introduced in commit
082fd9ff10b.

With tabbed maps, code could typically look like this:

	m = new form.Map('foobar', _('FooBar'));
	m.tabbed = true;
	s = m.section(form.TypedSection, 'foo', _('foo Settings'));

The problem is that the title of "s" will be used as the name of the tab
rendered in "m", but also rendered as an <h3> right below the tab. IOW,
the same information will be presented twice, which looks weird.

Doing this instead...

	m = new form.Map('foobar', _('FooBar'));
	m.tabbed = true;
	s = m.section(form.TypedSection, 'foo');

...means that the superfluous <h3> won't be rendered (since "s" has no
title), but the tab will then simply have the name of the section
("foo"), which can't be translated (bad).

After this change, the tabbed map can be written like this:

	m = new form.Map('foobar', _('FooBar'));
	m.tabbed = true;
	s = m.section(form.TypedSection, 'foo', _('foo Settings'));
	s.hidetitle = true;

Which will give the Map tab the name "foo Settings", but won't add a
title for the TypedSection right under the tab.

Signed-off-by: David Härdeman <[email protected]>