Split repository and rename entities

[mariyadavydova]

If we assume that our customers will use them as starting points, then forking a repo is much more convenient than copy-pasting code. Also, having them in separate repositories makes community contributing easier.

Let's stick to 'ML Recipe' and 'Cookbook' terminology from now on for an individual project and a collection, respectively.

So, I suggest to do the following:

• Put each recipe in a separate repository called 'ml-recipe-XXX'.
• Rename this repository to 'cookbook'.
• Make other repositories submodules, tracking head of master branches.
• Update READMEs accordingly.

[astaff]

Some readme updates have been made, but the whole suite needs to be tested end to end. @mariyadavydova please do it and make final updates to README. Can be a separate PR. Thanks.