[TM-279] Deprecate instructions which shouldn't be used in 005

Description

See https://blog.nomadic-labs.com/michelson-updates-in-005.html.

• STEPS_TO_QUOTA is deprecated.
• CREATE_ACCOUNT disappears.
• CREATE_CONTRACT changes type.

We want to prevent new code from using these instructions.

Solution: add warnings when these instructions are used.

Code in morley is not touched, because usages of these instructions there are fine, we are forced to use it when we process a contract supplied by a user which contains one of these instructions.

Also slightly updated the description of ceNow field.

Apart from that I've updated our branching policy according to what we've decided internally.

Related issue(s)

https://issues.serokell.io/issue/TM-279

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