Use IronScrollManager and actionProperty

[valdrinkoshi]

Fixes #127,
Fixes #126,
Fixes #120,
Fixes #112,
Fixes #101

Use IronScrollManager from iron-overlay-behavior, deprecate IronDropdownScrollManager.

Now allowOutsideScroll sets scrollAction when toggled. Special handling for initial setup:

• on ready, scrollAction is kept as is if defined, otherwise is setup according to allowOutsideScroll value
• after ready, toggling allowOutsideScroll always updates scrollAction

TODO:

• update iron-overlay-behavior version after IronScrollManager and scrollAction iron-overlay-behavior#234 gets merged and released

[e111077]

Do you mind please linking to the PR that introduced this feature?

[valdrinkoshi]

The scroll manager has always been part of iron-dropdown (see history of the file), I've been working on keeping the document overflow untouched and preventing the events in this PR #93

Update: the scroll manager was introduced in 1.0 (see this commit)

[cdata]

LGTM 👍

[valdrinkoshi]

Will merge this as is, then change iron-overlay-behavior version in bower.json in a separate commit