feat(types): Deprecate the DBBackend variable in favor of the Tendermint Config's db_backend value.

[dwedul-figure]

Description

This replicates the changes in the Cosmos-SDK PR 11188.

This PR deprecates the types.DBBackend variable and types.NewLevelDB function. It replaces them with a new types.NewDB function that accepts a db backend parameter. Uses of NewLevelDB were replaced with calls to NewDB and the db backend value comes from the tendermint config db-backend entry. The simapp stuff doesn't have the tendermint config, so a config field and flag was added in order to know the db backend value to use for them.

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