one big aggregated table

first draft in excel file, sheet 2
(readme contains changes on import scheme
but aggregation is still the old version)
Added dimensions on relays to aggregation

See Excel Sheet 3
new aggregation stretegy on excel sheet 4
import schema updates

relay table:
_id removed (not necessary anymore)
nid renamed to "node" (seems clearer)
span removed (not necessary in import tables)
type removed (not necessary in import ables)
"role" added instead of type (better name for relay types)
pex only relevant to exit nodes
client table:
the same where applicable
added comments from mailinglist

this is  just a first step to make sure essential parts from the mail
conversations aren't forgotten. the comments need to be weaved into the
text

some other rather minor changes
re-introduced '_id' and 'span' fields
incorporating some backgrounds about nodes, flags and such
blaa
sketch of aggregation in one big fact table
refining the aggregation outline

and correcting some mistakes in the import schema, mainly in the first
column (bgmedr)