refactor to add ICE and PCS evidence codes

[nlwashington]

there currently aren't real evidence codes for the ICE and PCS 3-letter codes used in the HPO data.

these have been requested in a ticket here: https://code.google.com/p/evidenceontology/issues/detail?id=32

they are currently mapped as follows:

  "ICE": "ECO:0000305",  # FIXME currently using "curator inference used in manual assertion"
  "IEA": "ECO:0000501",  # Inferred from Electronic Annotation
  "PCS": "ECO:0000269",  # FIXME currently using "experimental evidence used in manual assertion"
  "TAS": "ECO:0000304"   # Traceable Author Statement

when these get added to ECO, we'll need refine the dictionary definition in HPOAnnotations.py.