Remove different ways to run abci apps - only in process is required

[liamsi]

Description

Tendermint allows to interface with applications in different ways:

https://docs.tendermint.com/master/tutorials/go.html#built-in-app-vs-external-app

We only need to be able to run the application in process and can remove all other possibilities. While this looks like something we could easily do much later, @marbar3778 brought up a good point: namely that it would make our lives a bit easier with the e2e tests. More precisely, all different combinations (of app tests) are tested there: https://github.com/lazyledger/lazyledger-core/tree/master/test#tendermint-tests
e.g. https://github.com/lazyledger/lazyledger-core/blob/591d92bb1d1557bf9f9c3e7c7aa12be256009b4c/test/e2e/networks/ci.toml#L44

Removing some of the flexibility that tendermint provides, will make it easier for us to focus on LL and to more easily add e2e tests.

ref: #202

[liamsi]

Additionally to this, we should settle on a DB backend. Options are:
"goleveldb", "cleveldb", "rocksdb", "boltdb", "badgerdb"

(cc @tzdybal)

[Wondertan]

@liamsi, I think that the badgerV3 is the best option for present moment

[tac0turtle]

Additionally to this, we should settle on a DB backend. Options are:
"goleveldb", "cleveldb", "rocksdb", "boltdb", "badgerdb"

100% agree with this. Once we settle on a db we should look at optimizing for that specific DB instead of using the default.

Also agree badger seems to be best.

[tzdybal]

+1 for badger.

[liamsi]

I'm kinda surprised why everyone agrees on badger :-D Probably a very good sign. I'd like to better understand why badger is the best option before we decide on this.

[liamsi]

related:

• Supported database backends tendermint/tm-db#38
• Tendermint shows time dependent performance degredation tendermint/tendermint#1835 (comment)

[liamsi]

Let's continue the discussion in #211 instead. also, #208 resolves the original issue.