Replace isTypeOfException with actual Exception

[PawlikMichal25]

Currently there is no way to tell whether there was a connection problem during call to Parse - whether SocketException or other exception was thrown, because this information is scraped here, replaced with isTypeOfException and then mapped to -1: 'UnknownError'.

I would like to propose replacing isTypeOfException with the Exception itself, because it will be optionally providing more information than it is right now.

This is a small, but somewhat breaking change, so I wanted to open issue first and get your approval.
If you're happy with the change, I will open the MR :)

I actually did it some time ago on my fork of the project (please ignore removal of toString()), so you can see how the change would look:
https://github.com/BaranMichal25/Parse-SDK-Flutter/commit/01cba669925da613507eb6983679dc9a0e303b5f
We would prefer to use original library instead of my "private" fork, because it's a project for client, hence my proposal.

[phillwiggins]

Hey Baran

I actually like the idea and completely agree with it. Are you able to create a merge request with that branch, into branch labelled 'release/1.0.27' of this repository?

[PawlikMichal25]

Thanks, done here: #355