Make access request redirect to dashboard if user already has access

[timifasubaa]

With the access request feature, users who have access often revisit the access request page and are still shown the access request page.
This PR checks to make sure the user still doesn't have access before showing the access request page and redirects to the dashboard if they have access.

@john-bodley @mistercrunch

[mistercrunch]

I find the all and any functions much more readable than the &=, something like:
has_access = all((self.datasource_access(o) for o in datasources))

[timifasubaa]

done

[mistercrunch]

Watch out here, I'm pretty sure this dangling comma changes the structure from passing a tuple to all to, instead, passing it a tuple of one element that contains a tuple.

[mistercrunch]

It's a pretty common gotcha in python, v = 1, makes v a tuple

[timifasubaa]

@mistercrunch Looks like it's a quirk with Python consistency. I initially didn't have trailing comma but the flake8 rules required me to add it and somehow python reads it correctly. Also, the check is done correctly.

From my interpreter:

>>> all((True, True, True),)
True
>>> all((True, True, False),)
False
>>> all((True, True, False))
False
>>> v = 1,
>>> v
(1,)

I removed the comma anyway.

[timifasubaa]

PING

[mistercrunch]

Yeah I ran similar tests in an interpreter and still I'm confused as to how this works properly. I agree we cannot rely on this odd behavior as it may flap in the future or across python versions. LGTM