#1. made persisted storage exclusive to 1 process. like before, second VS with same solution will not use persisted storage.
#2, tweaked sqlite to share cache between connections like esent.
#3, made VS and OOP to use different db files (we can make them to share if we want to, but for now, nobody requires it so we create 2 different db)

..

made OOP mock to enable persisted service.

This is necessary now that several IDE features (i.e. FindReferences/NavigateTo) use OutOfProc by default.
If the server is not on, these guys just fall back and compute everything in-proc, defeating the point.

This also addresses issues where OutOfProc wouldn't be used even when it was supposed to.  For example,
if 'CodeLens' was off, but was then turned on, then OutOfProc still wouldn't be used.

this is to make develop - debug cycle easiler when adding new features to service hub.

to enable this, turn on Roslyn/FeatureManager/Features/RemoteHost and RemoteHostInProc

once enabled, InProcRemoteHostClient will be used instead of ServiceHubRemoteHostClient

except concrete type of RemoteHostClient, all other parts, exactly same code will be used.

InProcRemoteHostClient can be used in unit test to test client and server side as they are.

added abstraction in remote host and diagnostic service to prevent VS.Next dll from loading if remote host option is off.

the abstraction I added here is specific to diagnostic service feature. that abstract solely exist to prevent VS.Next dll from loading if remote host option is off.

this is different than IHostSpecificService abstraction I used to have that is generalized form of this abstraction which automatically figure out what to load based on option and layering/MEF composition of roslyn.

in this model, each feature need to take care of this kind of issue.