[Refactor] Move Appium capabilities to TESTAR settings

[ferpasri]

Status

We are currently using an external DesiredCapabilities.json file to indicate to TESTAR which are the Appium device's capabilities for connecting with mobile systems.

https://github.com/TESTARtool/TESTAR_dev/wiki/TESTAR-and-Appium-for-Mobile-Systems#running-testar-with-mobile-applications

Implementation

The refactor implementation must integrate these capabilities' configurations as TESTAR settings. Then, probably add a new tab in the GUI dialog.