Remove Babel 6 and support Node 10 across internal dependency graph

[rekmarks]

We should remove Babel 6 from and support Node 10 for all of our internal dependencies to avoid time-consuming problems when developing across packages.

These PRs have to be merged and their packages re-published in the following sequence:

1. Move Babel/Browserify to devDependencies, update packages obs-store#8
2. Escalate errors on RPC responses json-rpc-engine#18
3. Update packages, Babel 7, Node 10 eth-json-rpc-middleware#12
4. Update packages, Babel 7, Node 10 eth-json-rpc-infura#13
5. Update packages, Babel 7, Node 10 eth-json-rpc-filters#9
6. Update packages, Babel 7, Node 10 eth-block-tracker#41
7. Update packages, Babel 7, Node 10 web3-provider-engine#318
8. Update packages, Babel 7, Node 10 KeyringController#32
9. Update packages, Babel 7, Node 10  eth-token-tracker#13
10. Update packages, Babel 7, Node 10 providers#5
11. Update packages, Babel 7, Node 10 core#145
12. Remove Babel 6 from internal dependencies #7037 (PR submitted)

All builds and tests succeed in all feature branches. Until gaba is published, building the extension feature branch requires a local copy of the gaba branch and using yarn link after building gaba.

Resolved all security vulnerabilities except one irrelevant and low-priority in devDependencies.

[bdresser]

cc @kumavis @tmashuang this will require some coordination and QA!

[kumavis]

took care of everything but gaba and #7037

[rekmarks]

Update, Gaba has been merged and published. Now tracking exclusively in #7037