resizing slides to 16:9, adding margin for speaker

[mb706]

The magic happens in style/lmu-lecture.sty:

• resize page geometry to 170.666666667 x 96 mm (default is 128 x 96)
• define new length \speakerwidth, indicating the size of the margin reserved for the speaker PIP
• add an overlay to the free space for logo and optional background color.

This is what it looks like:

With different margin colors (set by editing marginbg color in lmu-lecture.sty):

Smaller margin (set by editing \speakerwidth in lmu-lecture.sty):