Add support for id and inner attributes

[vipentti]

Resolves #204

Options.id allows users to specify the id that can then be
used with the new DOM API.
Options.inner allows users to specify attributes on inner
elements of components that support it.

I went through the list by @debois in #204. Only components that I really found needing support for Options.inner were Textfield as well as Toggles, both of them have input elements that the users can now add attributes to with Options.inner.

Most of the other components have users specify sections of content already and for those they can just use Options.id (such as Tabs and Grids). For other components there was really no clear inner element that would benefit from enabling this support.

As always looking for feedback and suggestions, especially if there is a component that could really use Options.inner support

[OvermindDL1]

What about Menu? I've had need to attach things to both the outer container div as well as the button itself that brings up the menu. Although this will not be needed if Menu is ever converted to be like ToolTip's where you 'attach' it, but currently it is not. :-)

[debois]

@OvermindDL1: @aforemny is looking into (some variant of) the attach idea, see here.

[debois]

We lost style, so this needs to be merged in master, not v7, yes?

Maybe keep the name style in v7, then switch it to inner in master, add the switch to a new file MIGRATION.md in master, where we collect migration notes for the eventual v8 release.

[vipentti]

Textfield actually does not expose Config so this is a MINOR change according to elm-package diff

[debois]

I made some minor line notes, but I like this. Merge it when you've settled the v7/master question.