Cache coordinates and place names for geolocation lookups

[jmathai]

When looking up a geolocation coordinate we can cache the value to limit the number of lookups needed. A few considerations to make...

• Store location name (i.e. Sunnyvale, CA) to a lat/lon pair
• Store a lat/lon pair (i.e. extracted from EXIF)

lat/lon pairs within a certain radius of a pair that's already stored should return the stored location name. (see gelocation.place_name). When a pair is not within a certain radius of a stored lat/lon pair it should be looked up against an API and stored.

// cc @zingo

[zingo]

Here is an initial version
#48
Currently database look up don't scale well, but I'm unsure if it is a real problem as it might not contain a lot of entry's. (In my test I got 84 entry's for about 1 year of photos, with some travels)
Some item needing input, mabe in this commit or in a followup commit if you like to keep each commit simple:

• Should I add a simple lookup runtime cache for 3-5 last items, I think most new photos added will be from the same or few areas.
• The 3km range, should that be configurable in the config.ini file or is that overdoing it?
• Should we cache Unknows locations so they do not need to be re-lookedup on?
• Spotted that the Db is created 2 times per image (one time before) and the db-files are re-read everytime.

Interesting project this one you manage to create something I longed for!!!

[jmathai]

Merged gh-48