Add DashboardMiddleware class
Update Microsoft.Owin package to 2.1.0
Dashboard middleware url fix
Migrate Dashboard/Home page to Owin pipeline
Migrate content files to Owin pipeline
Migrate other parts of HangFire Monitor to Owin

* Batch commands are not supported yet
* HangFire.Web merged with HangFire.Core
* There is no more HangFire.Web package
Target all projects to .NET 4.5

Some Owin methods available only for 4.5 version.
Remove WebActivatorEx reference from highlighter
Retarget Microsoft.Owin package to net45
Remove HangFire.Web.nuspec
Allow to build only master branch in AppVeyor CI
Make HangFire Dashboard fully working under Owin
Cosmetic for dashboard sources

* Added headers
* Simplified names
* Removed unnecessary stuff
Authorization filters for Dashboard middleware
Add OwinExtensions class to simplify configuration
Add authorization filters for dashboard middleware

* LocalRequestsOnly
* ClaimsBased
* RoleBased
Add single entry for HangFire components
Use lazy server instantiation in UseHangFire method
Job and authorization filters for UseHangFire method
Set response status code on authorization failure