Check National grid refs are transferred to SEAD

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BugsCEp stores National Grid References as TSite.NGR.
For each site, these need to be stored in SEAD in tbl_site_natgridrefs.natgridref with appropriate national grid reference method in tbl_methods.
E.g.
Irish sites according to
68 "The Irish National Grid System, established by the Ordnance Survey of Ireland." "Irish National Grid" 17 "Irish Grid Reference System"

UK sites according to
67 "The United Kingdom National Grid system, established by the Ordnance Survey under the name OSGB36." "OSGB36" 17 "UK Ordnance Survey National Grid"

A country may have more than one grid reference method historically.
These methods need entering into table methods with

Note: Although this structure might be overkill for most sites, it allows users to store/search on different grid systems for countries which have had multiple such. E.g. Older Swedish sites may be registered with RT90, but newer ones with Sweref99TM. Then again, a search on the correct grid ref will return a correct result without needing to know the system.

We should discuss implementation pros and cons...

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Phil will write mapping between BugsCEP and SEAD and add to import checklist.
Might be best to add to extra post import script https://github.com/humlab-sead/sead_change_control/blob/master/bugs/deploy/20191213_BUGS_IMPORT_POST_APPLY.sql as more complicated to work into Erik's program.