Initial GUI integration test suite using Skyfiber plugin

**Feature description**

Initial integration test suite .

**Is your feature request related to a problem? Please describe.**
Project does not have a test suite , hence some regressions have been detected along the way but after merging a features branches into `develop` . At present there is no way to ensure after merging a feature branch that user interactions that used to work before merging it will continue to work as usual or change according to expected patterns of behaviors .

**Describe the solution you'd like**
An initial test suite including known vectors for SkyFiber wallets.

Run test suite it on Travis .

**Describe alternatives you've considered**
Maybe there is a more specific way to do it when using [`therecipe/qt` library](https://github.com/therecipe/qt). Research needs to be done to figure out if functions in [QTest namespace](https://doc.qt.io/qt-5/qtest.html) are available to go apps . If they are the how to use it , otherwise what'd be the alternatives .

**Additional context**
This should cover the work done for #117 #114 #111 #135 #108 #56 #49 #48 #47 #46 #45 #43

CI might require the use of [xvfb service](https://docs.travis-ci.com/user/gui-and-headless-browsers/#using-xvfb-to-run-tests-that-require-a-gui) enhanced by other multi-platform hacks .

Since test run might be lengthy it may be better to run it on Travis only before release.

**Possible implementation**
All details not clear to me . Consider reading [QT testing tutorial](https://doc.qt.io/qt-5/qtest-tutorial.html) .