Add Go test CI

[sebastianst]

We should write a Go test (TestClient) for the prnm package:

First we need to setup a CI config

• with a container where golang and nodejs are available,
• caching of go and node packages
• installation of ganache-cli at the beginning

Then the test itself

1. Create two fixed configurations for two test roles Alice and Bob (either as (alice|bob).json in directory testdata using Go's native JSON unmarshaling, or as fixed vars of type *Config).
2. Start a ganache-cli with os.Exec and a fixed mnemonic (-m).
   • Set alice's and bob's account in 1. to two accounts from the ones being created with this mnemonic. (only needs to be done once while doing this)
   • parse the output of this os.Exec until the test blockchain is setup
3. Start two go routines for alice and bob (see also go-perun's client/happy_test.go)
   • both create client from config
   • one of them deploys the contracts
   • alice adds bob as a remote peer (AddPeer)
   • alice proposes a channel to bob
   • bob accepts
   • both send TXs back and forth
   • one sends a finalization request
   • both settle the channel
   • channel and client are Close()d.
4. Perform balance assertions, similar to happy_test.go.

[ggwpez]

First step would be to automatically generate the bindings, i created a Dockerfile with Android SDK+NDK, go and go-mobile. It is also currently building the bindings as example.
Still have to figure out how to get it all together.

[ggwpez]

Somehow the unit tests do not run when linked with the prnm.aar file.
https://github.com/golang/go/issues/35403 mentions this, not sure if i can fix it.

PS: Only the pure Java tests seem to be affected. Instrumentation tests on the Android Emulator work.