Automatically load frameworks.

- Extend ObjectiveCFrameworkAttribute to accept a list of required frameworks
- Update all Monobjc assemblies to specify their required frameworks.
- Update ObjectiveCRuntime.ScanAssembly to load the required frameworks.

These removes the need to explicitly call ObjectiveCRuntime.LoadFramework.
Make auto loading frameworks configurable

Assemblies can be configured with their framework dependencies which the runtime can process automatically when the assembly is loaded. This is the default behavior since most applications will need to load the frameworks for referenced assemblies and the runtime has the information to do it. In some embedded environments assemblies may be loaded into the AppDomain which aren't actually referenced, and in such cases it can be useful to explicitly load required frameworks manually.
Merge branch 'feature/auto-load-framework' of https://github.com/spicypixel/monobjc into spicypixel-feature/auto-load-framework
Use explicit type.
There is no need for Linq.