Updated regular expression for both absolute and relative static file urls in nbconvert latex output
Added tests to filters/tests/test_latex.py for strip_url_static_file_prefix
Updated sphinx template to use both strip_math_space and strip_url_static_file_prefix in block markdowncell before markdown2latex
Removed strip_math_space and strip_url_static_file_prefix from preprocessors. Also removed test for strip_math_space in preprocessors/tests/test_latex.py