better method for handling patches where taxon no longer exists

[kcranston]

When applying the patches in curation/amendments.py, the whole build fails if the target taxon does not exist. The current fix seems to be adding a call to maybeTaxon before the patch, e.g. changing:

ott.taxon('Reptilia').hide()

to

if ott.maybeTaxon('Reptilia') != None:
        ott.taxon('Reptilia').hide()

this means you have to wait for the build to fail to see which ones need to be changed. Would be better to have methods that checked for existence of the Taxon and simply printed a message to the logs if the patch could not be applied. (Also, the current construct leaves no trace of patches that were not applied because the taxon in question does not exist).

[jar398]

this would be better done as an extension to the 'new' patch system
https://github.com/OpenTreeOfLife/reference-taxonomy/blob/master/util/proposition.py
for which name non-resolution is not catastrophic.