predictLogL function and corrected predictLVs

[dwarton]

• predictLVs.gllvm function corrected to handle new data of different size to dataset from original fit.
• predictLogL.gllvm function created to compute logL for new predicted values. Note though this seems to be very unstable, and slow, nRuns needs to be set to 10ish to get sensible answers for most new observations [consider allowing fits to data with columns of zeros, this caused problems].
• citations updated in DESCRIPTION and gllvm.Rd.
• other gllvm.* files not changed (at least, not intentionally!)