OAuth is currently not user-friendly

[codebru]

Background

This follows on from #17
It is also useful to be aware of influxdata/chronograf#4575

Issue

Chronograph currently has no login as default, and needs OAuth to be secure. The github OAuth setup is not ideal because of the following:

• Still open for anyone to log on unless a gihub org is set
• Then is available to everyone in that org
• The above is not ideal for setting up for a non github using organisation
• The steps for logging on involve giving access to the org but this is not prompted and if the user does not do it, it throws no error and just loops back to the login screen with no explanation.

Proposal

This is low priority at the moment, but it would be worth investigating other set ups at some point.