Upgrade to React 16.3 and migrate away from deprecated lifecycle methods

[cjcenizal]

See elastic/kibana#17432 for more info. I think this issue should be blocked until that issue is resolved so that we don't introduce incompatibilities with Kibana.

CC @chandlerprall

[chandlerprall]

We should be able to address the deprecated lifecycle methods without impacting downstream users.

[chandlerprall]

Talked with CJ more; we'll split this up into 3 phases:

• identify instances in EUI that use the deprecated lifecycle methods, mark them with // TODO React 16.3 and when possible add some thoughts on how the instance should be updated
• update components to the new lifecycle methods
• after downstream projects (e.g. Kibana) have updated to 16.3 address the remaining instances and update EUI's react peerDependency to ^16.3 (Kibana already updated)

[chandlerprall]

Kibana has been updated to 16.3, no blockers for this.

[chandlerprall]

All EUI components are updated off of the deprecated lifecycle methods.

[snide]

Nice work!