Round the numbers in the ANALYZE data

this makes it less intimidating to make up numbers for
future indexes, makes it clear that the numbers are
used as estimates, and overall seems to make the meaning
more clear.

Suggested by mvogt.
Merge pull request #183 from amtep/master

[performance] preseed ANALYZE data in the db
Introduce QueryBuilder class

This class will help simplify the code in contactsreader
to allow more flexibility in constructing queries for
performance reasons.

This commit just introduces the class and its tests,
it does not take it into use yet.