Add `isLoading` to frost-select

[EWhite613]

Overview

Add isLoading to frost-select

Screenshots or recordings

Please provide screenshots or recordings if this PR is modifying the visual UI or UX.

Semver

This project uses semver, please check the scope of this PR:

• [ ] #none#
• [ ] #patch#
• [x] #minor#
• [ ] #major#

Examples:

• NONE
  • README.md changes
  • test additions
  • changes to files that are not used by a consuming application (.travis.yml, .gitignore, etc)
• PATCH
  • backwards-compatible bug fix
  • nothing about how to use the code has changed
  • nothing about the outcome of the code has changed (though it likely corrected it)
  • changes to demo app (/tests/dummy/)
• MINOR
  • adding functionality in a backwards-compatible manner
  • nothing about how used to use the code has changed but using it in a new way will do new things
  • nothing about the outcome of the code has changed without having to first use it in a new way
  • addition of new CSS selectors
  • addition of new ember-hook selectors
• MAJOR
  • incompatible API change
  • using the code how used to will cease working
  • using the code how used to will have a different outcome
  • any changes to CSS selector names
  • any removal of CSS selectors
  • any changes to ember-hook selectors
  • possibly changes to test helpers (depends on the changes made)
  • any changes to the dependencies entry in the package.json file

CHANGELOG

• Feature add isLoading to frost-select and frost-multi-select