Use private fields in pkgconfig files

See merge request !8

configure.ac, ax_check_zlib.m4: updating autotools to add flags for zlib. these were removed upstream from lalsupport.

gstlal_itacac.c: fix bug where you try to flush more samples than we have from an adapter in a corner case

cbc_template_fir.py: use ChiWai's implementation if pandas is available, default to Chad's implementation

	--ensuring the template autocorrelation vs time is plotted with same length.

lloidhandler.py: Make the horizon history 1 day instead of 1 week for uploads.  This reduces file size to 5 MB which is highly desirable but also doesn't detract from e.g., making plots.

- temporarily clip the horizon distance history to just the last week when
  uploading to gracedb.  this will be reverted when a more efficient
  encoding scheme can be found