Added user account creation in Dexter VS plugin

[KarolAntczak]

When user provides correct server address but wrong credentials and clicks 'OK', a following message appears, allowing to create new account:

After clicking 'yes' a new account is creted, indicated by appropriate message:

Also, fixed issue #142

[KarolAntczak]

@mdopark OK, this is now performed by DexterClient (I added appropriate function) and doesn't require dexter jar. Also I found a little bug in server - fixed it.

[KarolAntczak]

@mdopark I refactored DexterClient so it is not a singleton anymore. I also modified its methods to return HttpResponseMessage, so it is easy to verify and handle result of the request.

[KarolAntczak]

I added missing [Export] attributes to DexterClient and SettingsStoreDexterInfoProvider classes.

This allows to add instances of these classes to PeerReviewTaggerProvider at runtime. I added unit test (PeerReviewTaggerProviderTest) which illustrates this idea.

[mdopark]

@KarolAntczak Hi, Karol. Thanks for your fix. Unit test runs normally, but PeerReviewTaggerProvider.CreateTagger () still does not execute. This method is executed by the VS editor when opening a document. I confirmed that this method executes normally, after deleting import related code.

And httpClient is not created every time in DexterClient, it seems to have to create the instance of DexterClient each time it calls the related method.

[KarolAntczak]

Oh, thank you, now I see where the problem is. I will fix it soon.

[KarolAntczak]

I fixed this issue. Now CreateTagger() executes properly when opening a document.

[mdopark]

@KarolAntczak Thansk you. I confirmed CreateTagger() excutes properly. But I have an error about DexterClient. After merging it, I will correct this error.