Increase tagline spacing (Issue 3214)

Spacing from the tagline to any text is far too small to be pleasing.  This patch increases it to be far more reasonable.

[PhilEHolmes, 2013-08-11 09:16:35]

Please review

[dak, 2013-08-11 09:58:10]

https://codereview.appspot.com/12562050/diff/1/ly/titling-init.ly
File ly/titling-init.ly (right):

https://codereview.appspot.com/12562050/diff/1/ly/titling-init.ly#newcode15
ly/titling-init.ly:15: \vspace #1.5
Inside of a line, this does not actually _add_ space but is more like a "strut":
a non-spacing element that has a height of 1.5 lines.  It will not likely change
with font size etc, and it will be part of the point-and-click area for
\with-url.

I'm not sure this should not actually rather be inside of markup-up-headfoot: it
would seem to make some sense to pad to a constant height there in order to get
a fixed layout.

[PhilEHolmes, 2013-08-11 10:30:51]

Alternative spacing mechanism

[PhilEHolmes, 2013-08-11 10:32:06]

Alterntive spacing mechanism - please review.

[PhilEHolmes, 2013-08-12 10:58:28]

Regtests updated

[PhilEHolmes, 2013-08-12 11:00:46]

Updating 2 regtests to prevent new overflow.  Overflow would be expected, so
allowing one regtest to compress a little more by using lyrics with smaller
vertical extent, and getting rid of the tagline on the other, which is not
really appropriate for paper of this size.

[janek, 2013-08-14 11:53:51]

LGTM