Export to TSV with tabs

[ckindermann]

The current implementation of export to a TSV file does not escape tab characters. Consider the folllowing triple in UBERON:

obo:RO_0002120 rdfs:comment "N1 synapsed_to some N2 \nExpands to:\nN1 SubclassOf ( \n has_part some (\n ‘pre-synaptic membrane ; GO:0042734’ that part_of some ( \n\t‘synapse ; GO:0045202’ that has_part some (\n\t ‘post-synaptic membrane ; GO:0045211’ that part_of some N2))))"

The literal contains two tabs. If these tabs are not escaped when exporting to a TSV, then 'synapse ; GO:0045202’ that has_part some (\n and ‘post-synaptic membrane ; GO:0045211’ that part_of some N2)))) will be interpreted as values for the 'datatype' and 'annotation' column in LDTab.