added readme.txt to RavenDB.Database and RavenDB.Embedded NuGet packages about package version restrictions
Merge pull request #1693 from ppekrol/master

added readme.txt to RavenDB.Database and RavenDB.Embedded NuGet packages...
Added a blocking message informing the user that is action is taking too long and that the server is not responding.
When the server respond the UI is unblocked.
Merge branch 'master' of https://github.com/ayende/ravendb
Merge branch 'master' of github.com:ayende/ravendb into RavenDB-3013