Delete bogus Bing no data tiles from cache

Fixed an issue when importing a tile set that already exists would cause an error. When an imported set has a same name, it is renamed so the name is unique. The original logic had an error and was allowing the "new" set to be added with the same name, which would cause an error. In addition, if a new tile set brings no new unique tiles, it is now ignored.
Fixed an issue where the progress was based on the total number of incoming tiles but this total can change if a given tile already exists in the database (it is not added).

Download Speed Tweaks (+2 squashed commits)
Squashed commits:
[ff0ef7e] Cleanup (remove OpenStreetMap)
[370fa1d] Done (+25 squashed commits)
Squashed commits:
[9f3368f] Need to check how many instances of MapEngine are active.
[d557eac] Download Optimization
[392f50a] Almost there.
Trying to optimize download.
[a49d1d2] Settings
[a94be97] Mostly there. Needs to finish options and map thumbnail.
[38d5a0b] Downloading tiles and deleting sets
[81101b9] More UI Work
[c597d4b] Downloading tiles
[a815e35] Get rid of OpenMaps
[7e177ea] More reorg
[fa6b671] Start handling create tile set
Fix signal order when creating fetch tile task
[2a31f4d] Refactoring
[268b906] Renaming things
[947d66e] Fix resource load error.
[19e2de8] Adding MapBox
[c73e627] Preparing download
[87bbf22] UI Tweaks
[3c32a86] A lot of UI code done.
[ece8ce2] Starting to deal with tiles
[7f387bc] Save tile set
[f66f343] Adding more code
[4de3418] Working
[f0cc25d] Done for the night.
[2d1d86e] Added SQL database for holding out own tile cache.
[d405a87] Convert to camel case as this has been driving me nuts.