query optimizations

* create indexes for columns used in queries
* always use pre-computed way_area
  - add way_area column to tables lacking it
* create additional columns to store pre-computed values
* remove redundant vtm queries
* add columns to store simplified geometries
suppress_simplification config where appropriate
support applying db changes in single pass

A single pass through the tables makes the operation faster because
records only need to be written once.
remove no longer used post-import.sql
parallelize single pass update across tables
use partial indexes for new columns
no need to create trigger for water_polygons
simplify poi level calculation
places can be either points or polygons
add comments describing tolerance calculation
Merge pull request #63 from mapzen/query-optimizations-single-pass-update

Query optimizations