Initial version of a simple SQLite backend

The player can not work with predicates yet and the NuGet-Package System.Date.SQLite is now required (but not included in the repo)
Implemented SQL-based player predicates
Implementd an additional `Record` overload that takes an enumerable of events that are inserted in a single SQL transaction. This gives a speedup of approx 100x (yes, 10000%).
Merge pull request #4 from lcanis/master

SQLite Backend