Add building and caching of `cardano-http-bridge` in Travis conf file

[paweljakubas]

Context

We want to have CI set up for the new cardano-wallet in order to have a means to automatically build the code and run all our tests against the build. At this moment we decided to go with Travis, so we want to get the .travis.yaml from the previous cardano-wallet review it and remove all unnecessary dependencies to cardano-sl from it. Instead, we want to depend on cardano-http-bridge as a gate for receiving blocks from the mainnet/testnet.

Decision

In order to use this repo with cardano-http-bridge we need to add instructions for building and caching Rust http-bridge to .travis.yml

---

Development Plan

• I intend to review the build instruction locally
• I intend to review travis documentation about Rust to see if there's anything good to know about it
• I intend to add necessary build instruction of the http bridge in the build steps of the CI, trying to make it a job running in parallel from our compilation
• I intend to make sure that the cardano-http-bridge is within the available PATH such that we can refer to it in our various scripts.

PR

Number	Base
#64	master

QA

• cf PR comment