Revamp 'Choosing the right storage' article.

[dmkozh]

I just wanted to add some clarification on independence of storage types, but ended up revamping it completely:

• Remove/update outdated info (such as reference to Wasm being stored in the contract instance)
• Remove/rephrase/move around less relevant info. The old article had a very long and irrelevant diversion on the role of state archival, that has nothing to do with the purpose of the guide.
• Add a table that highlights the differences between the storage types
• Update sections dedicated to individual storage types
• Rewrite the examples in order to avoid demonstrating anti-patterns (like auth-less storage modificaitons) and demonstrate intricacies of the storage (especially the temp storage)

I still feel like some of the info might be too verbose, but I think this is still a step in the right direction in terms of the information usefulness.

[stellar-jenkins]

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[stellar-jenkins]

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[stellar-jenkins]

Preview is available here:
http://developers-pr1006.previews.kube001.services.stellar-ops.com