Binary view type selection from "Open with Options"

[zznop]

This PR adds the IsForceLoadable method to the BinaryViewType class. This was done to allow selection of binary view types for raw binary formats. It allows users to select binary views from the "Open with Options" UI regardless of whether or not BinaryViewType->IsValidForData returns true. IsForceLoadable returns false for all existing views, but can be overridden in new views for binary formats that don't contain any header information that can be used to detect compatibility.

Related PR: https://github.com/Vector35/binaryninja/pull/811