Finish maki icons (add more POIs/icons and throttle api calls)

[jancborchardt]

(reopening original issue by you @v1r0x ;)

Currently we fire too much calls to the overpass api (see owncloud-archive/maps#112 (comment)).
Also there are only 'must have' POIs. We should add some more, see https://github.com/owncloud/maps/blob/master/js/script.js#L1340-L1342 for the missing POIs

refs #13 and #46 as well

[tacruc]

@jancborchardt can we close it?

[jancborchardt]

Yep, thanks for checking through! :)