Until now, Echo tests had to be run from mediawiki/core folder.
Add an independant 'npm run selenium-test' entry point
for local development. It comes with a minimal wdio.conf.js file that contains
only non-default settings, and runs only specs from this extension.
This also makes it so that screenshots are saved to this repo's
log directory instead of core's.
Bug: T171848
Change-Id: I1396f8d856c6cb1ad9818abf4ba09a4fcefdcfdc
