Limit the number of prompts shown to the user

The extension does not control the order OR the number of prompts shown simultaneously. Potentially linter, formatter, test settings, conda env, etc. can show up at once.

There is an added problem of calling blocking prompts in activate, which can cause extension to load to fail silently. https://github.com/microsoft/vscode-python/pull/7633#discussion_r329846057

[karthiknadig]

An example of the issue:

Another thing to consider when we show messages, like do they even work. If i have no interpreter selected, where is the install flake8 going to install it? It is unclear from the message what is going to happen.

[DonJayamanne]

Not, much, it’s a bug in the code.

I take that back, a possible solution is creating a custom linter (we’ve done this in the past). Details here https://github.com/microsoft/vscode-python/issues/7702