Check and add some interesting tslint rules

[webmaster128]

Interesting stuff we do not use yet: microsoft/TypeScript#29288 (comment)

[webmaster128]

Those rules that require type information that are not available in the current TSLint plugin for VSCode:

• no-unnecessary-type-assertion
• deprecation
• no-floating-promises
• strict-type-predicates
• promise-function-async

Since we don't want to lint in every build due to performance reasons, we first need to migrate from vscode-tslint to vscode-typescript-tslint-plugin. See differences with the vscode-TSLint extension

[webmaster128]

But when we have no-floating-promises, this code

export function foo(): void {
  sleep(3);
}

leads to

ERROR: (no-floating-promises) /iov-core/packages/iov-bns/src/bnsconnection.spec.ts[60, 3]: Promises must be handled appropriately

Great stuff!

[webmaster128]

Done in #789

Skipping strict-type-predicates as it does not work well with all our type checkers that use fake casts.