Add FileUtills::GetUserProfileDirectory()

This commit adds the FileUtills::GetUserProfileDirectory() function to
FileUtills.

(Again, Linux only as per usual. (I need to start porting these.))
Add FileUtills::GetCurrentWorkingDirectoryPath().

This commit adds the FileUtills::GetCurrentWorkingDirectoryPath()
function to FileUtills.

(It also fixes a missing reference typo in
FileUtills::GetUserProfileDirectoryPath().)