WIP: Modular AnteHandler

[AdityaSripal]

Addresses Issue #4572. Uses modular manager to execute module-antehandler functions in fixed sequence.

Will allow modules to define their own ante-logic and then applications can compose these functions easily to create the application's antehandler

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• Linked to github-issue with discussion and accepted design OR link to spec that describes this work.

• Wrote tests

• Updated relevant documentation (docs/)

• Added a relevant changelog entry: clog add [section] [stanza] [message]

• rereviewed Files changed in the github PR explorer

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[fedekunze]

@AdityaSripal does #4844 address this problem?

[alexanderbez]

@fedekunze no, they're somewhat orthogonal issues.

[golangcibot]

Error return value of acc.SetCoins is not checked (from errcheck)

[AdityaSripal]

Closing in favor of SimpleDecorators in #4942