shall we rename X-offset (and similar) to lowercase?

[Janek Warchoł]

Hi,

virtually all grob properties are lowercase words separated with
dashes.  I think we should get rid of exceptions to this rule and make
all grob properties lowercase - here's a list of offenders:

minimum-[XY]-extent
self-alignment-[XY]
simple-Y
[XY]-extent
[XY]-offset
X-positions
potential-X-colliding-grobs
pure-Y-common
[XY]-colliding-grobs
system-Y-offset

besides bringing consistency into our namespace, such conversion would
also save us some keystrokes (you won't have to press shift) - that
may sound negligible, but personally i find it a nuisance when i have
to write uppercase X and Y all the time.

Thoughts?
Janek