Refine transliteration pairs: the SRC must be on the left, DEST must be on the right

[ronaldtse]

Example:

Notice that in the *_NT column, the rows with values DS, NS, VS are always the name source, the rest are generated.

This task is to ensure the source is always on the left side, the destination is always on the right.

As described here:
http://geonames.nga.mil/gns/html/rest/lookuptables.html#Name%20Type%20Codes

NT_CD	DESCRIPTION	DEFINITION
C	Conventional	A commonly used English-language name approved by the U.S. Board on Geographic Names (BGN) for use in addition to, or in lieu of, a BGN-approved local official name or names, e.g., Rome, Alps, Danube River.
D	Unverified	A name from a source whose official status can not be verified by the BGN.
DS	Unverified Non-Roman Script	The non-Roman script form of a name from a source whose official status can not be verified by the BGN.
N	Approved	The BGN-approved local official name for a geographic feature. Except for countries with more than one official language; there is normally only one such name for a feature wholly within a country.
NS	Non-Roman Script	The non-Roman script form of the BGN-approved local official name for a geographic feature. Except for countries with more than one official language; there is normally only one such name for a feature wholly within a country.
P	Provisional	A geographic name of an area for which the territorial status is not finally determined or not recognized by the United States.
V	Variant	A former name, name in local usage, or other spelling found on various sources.
VA	Anglicized Variant	An English-language name that is derived by modifying the local official name to render it more accessible or meaningful to an English-language user.
VS	Variant Non-Roman Script	The non-Roman script form of a former name, name in local usage, or other spelling found on various sources.