Double resolution of regions from 1° to 0.5°

[ttencate]

This would help to reduce the number of gulls for people whose garden happens to be near the coast, for example.

How much extra data would this cost? Currently according to sqlite3_analyzer the regions table is about 2.2 MB, so I'd expect this to grow at most 4×, which would be up to 8.8 MB (probably less because not every quadrant would include all species of the original cell). This is still fine because the Play Store reports an app size of 138 to 139 MB at the moment (limit is 150 MB).

If needed, we can apply some clever compression. I just naively tried gzip on one of the longest entries, 1124 bytes, but that results in 1117 bytes. Maybe shorten species IDs using Huffman encoding; after all, we are spending 16 bits to represent only 800 species (~9.6 bits).