Fix bad parameter calling findByTipTaxa
Tweak fetchMultiTreeNodeId for async.map
Remove unused var
implement fetchMultiTreeNodeForMRCA

Given two node ids in the multitree, use the
getMostRecentCommonAncestor procedure to get the MRCA
Starting to implement findByTipTaxa

Currently requires two taxa

1. Converts taxon names to NCBI IDs
2. Gets the multi tree node id for each taxon
3. Gets multi tree node for MRCA of taxa

Next:

1. get ancestors from the taxa
2. return all calibrations associated with ancestorsA, ancestorsB, and
mrca
Add failWhenNotFound option to getCalibration

false by default. Allows map to succeed even if a single calibration is
not found
Set to true in findById
Uniquify calibrationIds and filter nulls

Prevents duplicates in the result set, and removes nulls when a
calibration id does not correspond to any calibration in the database.
Implement findByTipTaxa with 2 taxa

Some TODOs about checking inputs and still need to handle the single
taxon case
Support for single tip taxon search
Error checking for missing taxa and nodeIds
Merge pull request #5 from dleehr/filter-tiptaxa

Implement search by tipTaxa