Added support for EXIF lat/lng

I needed support for my web app to pull lat/lng data from uploaded images, so here you go.

This patch adds two new metadata fields: ```latitude``` and ```longitude```.

EXIF lat/lng data is stored as an array of DMS values, not decimal, so this also adds a new function ```dmstodec()``` which converts this array into a decimal value you can easily store in a database.