Implement Multi-Tenant DbContext for SQLite With Db Expiration

[deyvidnenchev]

If user of the Northwind API want to use his own dataset (not modified by other users) he has to include X-Tenant-ID header.

1. Add the ability to have fresh database based on X-Tenant-ID header of any request to Norhwind API
2. Add DB expiration (SqlLite:memory)
3. Add validation middleware for X-Tenant-ID header
4. Remove InMemory Database option (useless because relations don't work)

[pmoleri]

We should test if everything goes fine when multiple requests to the same tenant are done concurrently.
e.g. an App Builder view loading a category, products and orders grids at the same time.

Especially considering the seeding case, when there's not connection yet (or it has expired already).