DB reader update, API throttling

[wwwMADwww]

Hello!

The main goal of this PR is to fix *.db file reader, now it can read files with version 20191106 and later.

Unknown properties like SomeBool, Byte, Byte2, etc renamed, DbBeatmapStatus enum entries slightly changed, added enum for UserPersmissons, all this according to osu wiki.

Regular Int32 Enums now can be saved as Bytes, unfornunately your commit mentioned here did not fixed this.

NotImplementedException added because i tried read-write to osu!.db and this always results in file with less data than i just read, turns out WriteValue for binary dictionaries is just empty. Absense of exceptions or at least console message here was very confusing.

API repositories now can be throttled. In practice it seems to be not needed today, but i already implemented this. Maybe would be usefull in multithreading.