[jarun#698] fixed dependencies & improved testing time

[LeXofLeviafan]

fixes #698:

• adding a limit on werkzeug library version (dependency of Flask-API) to fix compatibility problems
• moving return statements out of the (unnecessary) finally: blocks

also:

• modifying tests to avoid unnecessary network requests (this was causing very long freezes in some tests)

[LeXofLeviafan]

As a bonus, pytest runs take much less time now (from ~260 seconds down to ~50)

[jarun]

Thank you!