Upgrade .Net Core SDK from '1.0 Preview 2' to '1.1.5' (this is the LTS branch) and from Visual Studio 2015 to 2017

[bergmeister]

Closes #821
I chose .Net Core 1.1 because this is the current LTS branch of .Net Core. Would you prefer 2.0 (this would have the advantage of having more APIs and the automatic dotnet restore)?
I found that the resource auto generation broke after upgrading using dotnet migrate and I could not figure out why at first and therefore adapted it to make it possible to use Visual Studio for that. During this process I found that the reason for that was that I had to add properties in the csproj files to make the default assembly name match the namespace. I removed the calls to the ressource generation script but adapted it so that it still works.
The build scripts were also improved to restore the first time. From a fresh new checkout, one can simply open the solution in Visual Studio and it builds out of the box without any initialisation steps apart from having .Net Core 1.1.5 installed.

This PR is now ready to be reviewed.

[JamesWTruher]

I'm sorry about letting this go so long, I'm still coming up to speed on the repo. Now that Core is up to 2.0, should we do this, or just jump to 2?

[bergmeister]

We could go to version 2 but the reason why but I was unsure it because due to the increase of the API surface, this means that there are less devices on which it could potentially run on. But maybe this does not apply to PSSA since mobile operating systems are not involved similar to PowerShell Core.

[JamesWTruher]

yes, i'm not sure where this would run in the absence of PowerShell or PowerShell Core. Should the version of the SDK just track to PowerShell Core framework version? Definitely coming off of 1.0-p2 is great

[bergmeister]

Then we could go to v2 except that there is the risk that it brings breaking changes that do not get uncovered by tests. Maybe this should be a separate PR? Also the version should probably be not be higher than the one that 6.0.1 ships with because I do not think that one can run a cmdlet built in a newer version of the .net core runtime than pwsh itself?

[JamesWTruher]

re: agree about not being in front of 6.0.1, with regard to v2 compatibility I don't have a good handle on utilization, but remaining compatible with v2 is perhaps not something we should worry to much about as that is so old a version of PS. (IIRC, even Pester has left that behind with the release of 4).
The other open question is about release updates - how often do you think we should do that? Calendar driven? Feature/Functionality?

[bergmeister]

OK. I opened a new issue with the intent of having a 2nd PR with the upgrade to 2.0 (in case it turns out to be more complex than anticipated).
About the releases: Personally speaking, feature driven would make sense (or if a newer version of PowerShell Core makes breaking changes that require fixes).

[JamesWTruher]

we'll do this on the way to 2.0