expose auth0 instance and more coverage for auth0 API

[dan-harris]

[ ] Regression
[ ] Bug report 
[ ] Support request
[x] Feature request
[ ] Documentation issue or request

Current behavior
Firstly, big thankyou to @fulls1z3 for this great wrapper library. Works like a charm! However, currently ngx-auth doesn't allow us to use some of the other great auth0 methods that are available on the internal auth0 instance. As an example; passwordless login/signup, programmatic login/signup, checking/renewing the current session.

Expected/desired behavior
I propose that ngx-auth both exposes the internal auth0 instance, plus provide a few extra 'wrapper' methods (e.g. session renewal).

What is the motivation / use case for changing the behavior?
Providing access to the inner auth0 instance means the developer is able to use the auth0 api directly if they need, plus create some of their own functionality if needed.
Creating more wrapper methods means ngx-auth becomes a more feature-rich wrapper, whilst still handling some of the annoying parts for you (e.g. abstracting away the storage of access tokens & id tokens .etc).

[dan-harris]

By the way, happy to put this feature through as a PR if approved.

[dan-harris]

Hey @fulls1z3 - any chance you'll get a sec to think about this?

[dan-harris]

@fulls1z3 - thanks for updating to Angular 7 and raising the enhancement. Would you like a PR for the functionality? Or is it something you;d like to take on?

[fulls1z3]

@dan-harris first of all thank you very much for your appreciation, and sorry about reacting late.

there was a moment i couldn't contribute to Open Source - sometimes time really doesn't allow us to do anything.

i'm going to have a repass on the core functionality, and on the other hand feel free to make contributions. meanwhile, i contacted Auth0 team for some kinda demo access (full features) - and as soon as i get some answer we'll be able to test further functionality.

all the best!

[dan-harris]

No problems at all. Appreciate the effort you've put into this lib.... understand you're putting your own free time into it 👍

If you're going to be re-doing some of the core stuff, I might wait until then. After that though, might throw a couple of additions in a PR (if you haven't already added them)

[fulls1z3]

@dan-harris sorry for the delay, had busy times. feel free to fire a PR and i'll approve.