Fix shebang lines and make them more consistent.

[jebrosen]

On linux (I am not sure about macOS), #!/usr/bin/env perl -w attempts to run a program literally named perl -w which does not exist. Shebang lines are now:

• Moved to the very first line of the file, where they are guaranteed to be found by the shell
• Always #!/usr/bin/env perl

Scripts that had perl -w now have a use warnings; line.

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This should only really be necessary for scripts that might be invoked from other programs i.e. LAI and LTR_Retriever, but this change can benefit anyone who might try to reuse or work with the scripts in bin/.

[oushujun]

Thank you very much for fixing the shebang line!