Support for loading/editing/saving .NET Core single file publish bundles. (#16)

[ElektroKill]

This PR aims to bring support for loading, editing, and saving .NET Core single file bundles.

Current implementation status:
dnSpy is able to display assembly entries of bundles and allows editing and saving said assemblies (excluding hex editor).

Roadmap:

• Fix AssemblyResolver to work properly for assemblies inside bundles.
• Iron out some of the remaining jump to reference bugs (e.g. namespaces).
• Pass the embedded symbol files to dnlib to provide additional information to decompiler.
• Add support for editing the single file bundle itself .
• Add support for showing all the other entries a bundle can have in the tree view.
• Add Hex editor support for the embedded assemblies.
• Bundles can have folders inside them, these need to be replicated in the tree view.
• Debugging support for bundles.

Some of these regular dnSpy features require the file to be present in the filesystem. An example of such a feature is the Hex editor. I'm still debating whether support for this feature should be left out or should we write the extracted bundle entries to disk in a temporary location.

fixes #16

[ElektroKill]

This feature will not make it into dnSpyEx 6.2. I severely underestimated the difficulty of properly implementing this feature. Furthermore, I kind of lost interest in implementing this feature so for now it will be placed on hold. Sorry!