Pull ProcessInfo and ProcessLaunchInfo out of Target/Process.

Elevate ProcessInfo and ProcessLaunchInfo into their own headers.
llgs will be using ProcessLaunchInfo but doesn't need to pull in
the rest of Process.h.

This also moves a bunch of implementation details from the header
declarations into ProcessInfo.cpp and ProcessLaunchInfo.cpp.

Tested on Ubuntu 14.04 Cmake and MacOSX Xcode.

Related to https://github.com/tfiala/lldb/issues/26.