Major "refactoring"

* Moving DTOs to separate project
* Moving DTO integration logic to repositories
* Adding cross platform project skeleton using Mvx and Portal Class Library
Updating xamarin projects to use mvvmcross from nuget
Reenabling web page concepts but leaving them in the old domain projects for now.
Setting up CI configuration for build script
Adding solution folders to clean things up a bit
Checking for null reference on book retrieved from bokbasen in imagerepository
Fixing hint path for xunit dll in core.tests project
Merge pull request #94 from dagolap/feature/domain_refactoring

Feature/domain refactoring