[dev] Upgrade mobx dependencies

[southerneer]

Current: mobx@3.3.1, mobx-react@4.3.5, mobx-state-tree@1.3.1
Latest: mobx@4.3.1, mobx-react@5.2.0, mobx-state-tree@2.0.5

We're a major version behind in all 3 of these vital dependencies. Probably the work necessary to perform the upgrade should be split into 3 tickets, but this will get the discussion started.

We would also need to investigate the breaking changes in each upgrade to determine the effort involved.

[southerneer]

@aksonov we would need to change RNRF to upgrade mobx and mobx-react. Have you given any more thought to changing those to peer dependencies in rnrf? Probably it's a matter of merging that PR and adding a warning/error message in RNRF if mobx is not installed.

[aksonov]

No need to create several tickets because all they are very coupled and depends each other - it is almost impossible to do one without others.

[aksonov]

Accepted that PR and published RNRF 4.0.0.beta.32

[southerneer]

Not directly QA-able.