update some defaults in latex style

[Bernhard Weichel]

Request

When using Wortsammer -pbi I would see some changes in the default behavior

• nofloat
• support \needspace
• prevent graphics from being distorted
• adjust tocdepth
• inject Variables in to the document - similar to snippets
• ability to scale images but keeping aspect ratio (see https://stackoverflow.com/questions/30098286/pandoc-disable-figure-stretching-from-markdown-to-pdf-conversion/30100389#30100389)
• specify the latex style-file
• image root

Best would be if this could be set in the yaml metadatablock