Add page numbers to footer

I use a simple pagenumber in footers. See

- http://wiki.contextgarden.net/Headers_and_Footers

for details.
Change background color

I remember reading somewhere that white is not a good color for slides. So, I
change the background color to lightgray. See

- http://wiki.contextgarden.net/Command/setupbackgrounds

for more details.
An example for bullet list

The item marker is not shown because the default item marker is picked from the
math font and Neo Euler math font is not complete, so that marker is missing.

In the next few steps, I will show how to use a different item marker, so lets
not worry about it right now.
Setup itemize head style
Use metapost to create a item marker

For more details on using MetaPost, read:

- http://wiki.contextgarden.net/MetaPost_in_ConTeXt
- http://www.pragma-ade.com/general/manuals/metafun-s.pdf

For details on symbols, read:

- http://wiki.contextgarden.net/Symbols
Set spacing for itemize

Tweak the spacing around bullet according to your preference.
Example for nested bullet list
Tight itemized list for level 2

By default, lists in ConTeXt are `unpacked`. I prefer to use second level lists
without any additional spacing around the items; hence the `nowhite` option.

This setup is not perfect because of the extra space before the 2nd level
items. This will be fixed in the next commit
Remove unwanted spacing before 2nd level list

To remove the unwanted space before the 2nd level list, an non-interfaced
setting needs to be changed.

There might be a better, higher-level way to get the same visual output, but I
am not aware of it.
Set 2nd level itemize marker

Again, this is a matter of personal prefernece. I use MetaPost to draw a
triangle as a second level itemize marker
Set document metadata

Simply set the metadata. The next few commits will show how to use this
metadata.
Add metadata to footer

Again, this is a matter of personal choice. I like to include the presentation
title and the author in the footer of each slide. Read:

- http://wiki.contextgarden.net/Headers_and_Footers

for details on setting the footer and

- http://wiki.contextgarden.net/Inside_ConTeXt#Using_variables

for information on variables.