Scope can be configured in settings file

[puentesarrin]

Hey there!

These changes are useful in case someone wants to make scopes configurable by settings. For example, usually the following scopes are required for Google OAuth and right now it's not possible to make it configurable:

• "https://www.googleapis.com/auth/userinfo.email"
• "https://www.googleapis.com/auth/userinfo.profile"
• "https://www.googleapis.com/auth/plus.me"

Thanks in advance.

[puentesarrin]

Whoops, I just realized that there already is another PR for the same purpose but it adds changes on unrelated code. Looking forward to your comments!

[IvanAnishchuk]

I would really love having this (or, perhaps, the other PR) merged, now that django 2 is supported this is the only thing preventing me from using this library -- my auth service relies on custom scopes heavily.

The changes here seem to be pretty straight-forward and compatible with previous default behavior. Is there anything we can do to expedite merging? @kevin1024

[kevin1024]

Thanks for the nudge. Looks like a good feature. Merged.

[puentesarrin]

Thanks, guys!