ComputeFstat: small simplication of Fstat-API to use a single setup function

- removed method-specific setup functions for _Demod and _Resamp, instead
- use single XLALCreateFstatInput() function, passing the FstatMethod,
  which will internally perform method-specific setup as required
- adapted all affected lalsuite codes (CFSv2, Hough, Recalc, GCT)
- refs #543
ComputeFstat: documentation editing and minor fixes

- pass extraParams as a pointer to XLALCreatefstatInput(), for
  consistency with all the other struct parameters
- remove XLAL prefix from ComputeFstatFromFaFb(), to better
  distinguish it as an internal function (not part of XLAL API)
- use F-stat 'method' instead of 'algorithm' consistently in docs
- other minor reformatting and editing of documentation
- refs #543
ComputeFstat_Demod: fixed bug in buffering for different refTimes

- buffering previously didn't check if stored SSBtimes belonged to
  the same reference time as the current template for re-using
- this was exposed by 'luck' only by the different refTime usage
  in XLALComputeExtraStatsForToplist()
- fixes #1359
testHS: include checks for recalc'ed values with Demod method

- also outputs and compares the resampling recalced values, but
  accepts their failure for now, until this is also fixed.
- refs #1359