Add new PeakInvestigator external library and UTIL program

This pull request is to address the comments from @aiche in PR #1007. Specifically, I have placed the new library external to the core OpenMS library as suggested by him and others. I have also split the many of the non-PeakInvestigator code into separate classes:

1) TarFile, for bundling/extracting scans from a MSExperiment.
2) LibSSH2SecureFileTransfer and PSCPSecureFileTransfer, as well as their abstract base class, to simplify the code, especially by reducing the number of #ifdef statements.

The code complies on Mac and Linux (at least in my Ubuntu VM), and I am currently testing compilation on Windows 7 in a VM right now. I still need to add documentation and potential test methods, which will probably take me a few days. In the meantime, I would appreciate any comments.

Since it's a small part of the code, I (perhaps naively) assume that it's ok to use the struct and checksum function outside of the Apache License. Is that reasonable? If not, I'll move it to another file.

If I move it to another file, do you have suggestions for filename? Should I keep it as ```tarball```, or rename it to something more specific (```PosixTarHeader```)?