Play with Mento v2 script for swapping with local geth node account

[arthurgousset]

Convo with Mento is happening here:

• Mento V1 to V2 upgrade (`exchange` command) #5

Bug report here:

• cUSD exchange doesn't work  #75

Context from Slack:

We could play with the example Mento script (swap.ts) and see if using that logic is simple.
If it is, we can debate adding support to the CLI.
If it isn't, we can suggest users run the script without CLI support (and make sure it works well with accounts in a node).
It's just that adding support and then deprecating it shortly after, is suboptimal.
Ideally, Mento would speed up the delivery of their CLI.
Even better, Mento's CLI would be a plugin for celo CLI.

[arthurgousset]

Superseded by this:

• Exchange tokens via mento broker #106