Provide a way to determine the version/date of the latest release of Language Server

[DonJayamanne]

This is necessary to enable the following (microsoft/vscode-python#2580).

Basically all we need is:

• Is there a new version of the language server published online?

Proposal:

• Upload a text file latest_version.txt with the version info, to the location https://pvsc.blob.core.windows.net/python-language-server
• When ever VSC downloads a language server we can capture the latest version info from the latest_version.txt file
• Next time we just download the latest_version.txt and compare it against the previously downloaded info.
• If the new version is DIFFERENT, then we download the packages.

This sounds like a KISS solution. I don't think we should complicate it.
Either way, i'd like a very simple and easy way of determining this from the extension, hence the suggestion for the text file.

Also, I believe generating and uploading the text file can be automated into the CI pipeline. I.e. no coding, just CI.

[DonJayamanne]

@MikhailArkhipov
Please change the priority as you see fit.
I'd like to complete the VSC side of things early next week, if not monday :)

[MikhailArkhipov]

Related #97

[MikhailArkhipov]

@AlexanderSher handles the build definition so I am passing it over :-)

[MikhailArkhipov]

It is implemented