model: Added elevations table

Data can be added to the table through the built-in raster2pgsql script
scripts: Added import_srtm.py script
lib/sql: Added extract_array_item() function
model/flight: Set SRID for locations column to 4236
baro.js: Added elevations support
fix-table.js: Added elevations support
flights.js: Added elevations support
controllers/flight: Added elevations support
Merge branch 'master' into elevation

Conflicts:
	skylines/controllers/flight.py
controllers/flight: Import cleanup
baro.js: Limit the barogram to positive altitudes
flight.js: Convert elevation data to user units
Merge branch 'master' into elevation
baro.js: Move elevation data to the background
import_srtm: Use configuration file for database access
import_srtm: Use correct SRID for raster data
import_srtm: Use out-of-DB raster data

This can be much more space efficient and the speed disadvantage can be
fixed by caching the data properly.
import_srtm: Create tiled and compressed GeoTIFF files
Fixed SRID typos

WGS 84 is SRID 4326, not 4236
Merge branch 'master' into elevation