ConTeXt template:  Setup up defaults for floats.

This allows the user to adjust the figure and table placement
and numbering globally.
LaTeX template: Add booktabs package
Merge pull request #47 from jlduran/booktabs

LaTeX template: Add booktabs package
Beamer template: add booktabs package
Merge pull request #48 from lionandoil/master

Beamer template: add booktabs package
Added abstract variable in latex template.
latex template:  Put header includes after title.

Closes pandoc#908.
Fixing default.beamer includegraphics redefinition to allow custom options
Merge pull request #49 from lionandoil/master

Fixing default.beamer includegraphics redefinition to allow custom options