Infrastructure for tests with integration with RavenDB

I would have used http://www.nuget.org/packages/RavenDB.Tests.Helpers but nuget is misbehaving
Correct handling of numeric values

Critical/Processing/Delivery times were stored by strings. This commit stores them as numerics by using Ticks. Also using the null-value pattern for when there's no data to store instead of using 0's.
Minor
Revert some changes to rely on RavenDB's TimeSpan auto conversion
Attention: sorting will

This affects QueryableExtensions.Sort being used from GetMessagesByQuery. Need to figure out if this is a wanted effect; also, no secondary sorts are supported.
Merge branch 'develop' of github.com:Particular/ServiceControl into numeric-fields
Expose query staleness and performance from the API
Minor optimization

Removing a recursive call in on of the maps
Fix type in index name, prevent future mistakes by strongly typing
Reuse existing indexes whenever possible
RavenDB testing best-practices
Merge branch 'numeric-fields' into develop