Lenient http-spec

[P0lip]

Chore summary
The low-level goal is to make http-spec treat malformed input in a more graceful manner.
The high-level goal is to improve UX in Studio, in particular when you open an existing spec that's incorrect.

Tasks

• upgrade to TS 3.7
• use Optional<DeepPartial<actual shape>> whenever possible
• drop all calls clobbering typings such as lodash.get and use optional chaining operator
• add a couple of tests covering edge cases

Additional context
Prettier uses outdated typescript/es-tree parser and won't parse optional chaining operator correctly.
For the time being, suggest turning off prettier rule in TSLint config until they upgrade it.

[P0lip]

Optional<DeepPartial<actual shape>> might be look tad controversial, therefore if you all think it's an overkill, we can stick with DeepPartial<actual shape>.

[chohmann]

@P0lip is this issue still relevant?

[P0lip]

Yeah, it's still relevant.
The situation has improved over the time, but there is still plenty to be done.
FWIW, Vincenzo has context on this one, as we used to rant chat about it in the past.