Refactor LogFileData interfaces

Refactored parts of the io/logging module. The focus is on the LogFileData implementations. Closes #19 (closed)

New Features

• [io/logging]:
  • LogFile: Added file attributes, which may be used to store custom global data in log file headers / footers. This replaces the default log header implementation.

Breaking Changes

• [io/logging]:
  • Moved all column-based logging related stuff to ColumnBasedLogFileData
  • Refactored the interface of ColumnBasedLogFileData: The new ColumnBasedLogStream allows easy definition of data and header name in one place.
  • Removed unused return value of the encode methods