Nuget - Revert back to the 63 package props/targets files

The newer changes aren't complete - missing at least the BrowserSubprocess, so going with what's been tested for now.

Will fix in `master`

build.ps1 - Set assemblyversion to same as version when appveyor tagg…

…ed build (release build)

Update MyGet API Key

Previous key expired

JSB - JavascriptObjectRepository.ResolveObject was only being called …

…when object previously registered

The HasBoundObjects check has been removed, now we always attempt to GetObjects and return a response

Resolves cefsharp#2273

CookieManager - Make unmanaged constructor internal

MyGet Key Update

Update to using a limited access expiry key from my account (amaitland)

Nupkg Restructure

Resolves cefsharp#2156

Nuget packages updated to use ItemGroup None instead of Copy target
Nuget props restructure to support Win32 target
x86 and Win32 targets are exactly the same in content, they differ in name only, so switched to using an <Otherwise/> block
Remove AnyCpu <When/> option from props files and consolidate with x86 and Win32. Set Private to false and rely on the
<None/> entires to copy the files to the output folder

Ideally would move the OffScreen, WinForms and WPF targets file content to the props (as they're actually props now), unfortunately
we need guaranteed ordering and Nuget 2.8.x doesn't provide that, if we leave them as .targets it'll happen late enough to make sure
the cef.redist list of files is provided.
NuGet/Home#4229 (comment)

README.md - Add cefsharp/63 branch details

(branch to follow)

appveyor.yml: Update api_key

The previous key belonged to Alex Maitland, who has revoked it. Updating to use my own key instead.

Upgrade to CEF 3.2987.1601