ELAPI: Improvements to file provider
    
    1) Moved all the config code from file_provider.c
    to a new module file_config.c
    2) Added module that has framework to build
    headers for the files. This functionality is
    needed for CSV and HTML formats mostly.
    Headers can now be configured to appear
    on everey run, never or only on new files.
    3) Adjusted serialization functions
    to be able to use same code for main data
    and headers.
    4) Added configration of the headers.
    This includes configurable name for the leftover
    column, alternative names for columns etc.
    5) Addressed ticket #169
    6) Addressed ticket #225 - only permissions.
    After some thinking I am not sure we need to do
    something about the ownership.