Test fixes

[Ampretuzo]

This PR fixes all lint, type check and testing errors.

Some stuff is actually duplicate of this branch, since I had started to fix things independently and found it easier to go solo.

To do:

• [x] first of all, I need to test running local server manually to make sure I didn't introduce bugs during this fixup. (Did minor modifications in type check fixes that could affect the app.)
• [x] Either cherry pick and merge "can remove the first *" tests from this commit, or merge both PRs separately (@rschroll ) into newtemplate.
• [x] Jenkins CI!

PS type checking can really benefit us here!

[Ampretuzo]

I think we're good here, but I remember I thought so last time too. @rschroll, I would appreciate if you could do a simple test-drive of this branch.