Enforce TS strict type checking.

[Nerivec]

Require ZH: Koenkk/zigbee-herdsman#1146
Require ZHC: TODO

@Koenkk I'll let you check the HA extension, don't know much about what it's expecting on the other other side, so, didn't touch it much.
Settings are a bit nasty too. Seems there a need for a SettingsWithDefaults type or something similar, to avoid the many xyz | undefined that result from current typing?
And have to confirm the logic in zigbee.ts for resolveDevice and resolveEntity.

[Nerivec]

Note to self: all tests are passing locally in 4c7a5fa (ci fails because of build)

[Koenkk]

CI passes now, @Nerivec let me know if this can be merged

[Nerivec]

Should be good to go.
Some of the logic is a tiny bit different here and there, but we'll know if more coverage is needed from dev testers during the month.

I think an extra manual check is warranted in z2m, zhc, zh and frontend on the following:

• === undefined
• !== undefined
• === null
• !== null

Since a few occurrences changed from null to undefined, it could create weird behaviors (especially since a lot of stuff gets processed into js<>json). zhc and frontend definitely need "extra-extra-checking" on this since they don't have strict: true yet.

[Koenkk]

Great, I will hold it back for a couple of days, need to make a hotfix release.