Pkp-lib: Port integration testing framework to Cypress

[asmecher]

Our integration testing toolset is getting rickety. It fails intermittently and doesn't use a well-trodden stack (the Facebook/Chromedriver/PHPUnit combo seems just about unique to us).

Instead, try Cypress. It's widely used and claims to take integration testing out of async browser hell.

[NateWr]

I took a quick look at Cypress and it looks great! I noticed that we can change the viewport size during tests so that will be great for running mobile tests for the default theme. :+1:

[asmecher]

Progress: Tests working in OJS! https://travis-ci.org/asmecher/ojs/builds/634523305

Remaining work:

• [x] Statistics test needs to be ported
• [x] CI test (OMP) needs to be ported
• [x] Review OJS and OMP for additional tests not caught above
• [x] OMP test code needs to be adapted
• [x] Preprint server test code needs to be adapted (pull: https://github.com/ajnyga/ojs/pull/9)
• [x] Plugin tests need to be adapted (example: https://github.com/pkp/staticPages/commit/b7e5fb5519dc821ced525fae44ed8b64646d2773)
• [x] Improve performance -- the OJS suite appears to have gone from ~18 minutes to ~33 minutes :worried:

[asmecher]

Aaaaand we're done!