Create a library functions for handling paths in a microsoft safe way.

We currently have a lot of similar code for handling path strings that are from other operating systems (Windows). The current method is to do a string replace

str_replace('\\', '/', $path);

This code is used 56 times through the code, though a large amount of those are in third party files.
Use the following for a complete list:
grep -r "str_replace('\\\\\\\\', '/'"
git grep will show you areas only in core moodle.

It would be preferable if this was centralised in the one location.