Simplify support matrix.

[cibernox]

I just found that this addon has a lot of test scenarios:

• ember-1.10
• ember-1.11
• ember-1.12
• ember-1.13
• ember-2.0
• ember-2.1
• ember-2.2
• ember-2.3
• ember-2.4
• ember-2.5
• ember-2.6
• ember-release
• ember-beta
• ember-canary
• ember-alpha
• ember-data-2.3

Can we simplify that a bit?
I think that at least 1.10, 1.11 and 1.12 should go. Is alpha still a thing? When should 1.13 die?

If you agree I can give it a try. If anyone is aware of any code just to support some of the scenarios being removed please tell.

[rwjblue]

This project has lots of scenarios because we currently support all of those ember versions, if we intend to support them we should test them.

I'm happy to start having the discussion of dropping support for non-LTS and non-current releases, but we'd need to make that a 0.7.0 I believe.

[cibernox]

That sounds perfect. At least dropping support for 1.X seems advisable at this point.
The last 2 LTS releases seems reasonable policy to me, and that will soon be 2.8 and 2.12

[Turbo87]

this was addressed by #213